Decreasing lactate level and increasing polypeptide production by downregulating the expression of lactate dehydrogenase and pyruvate dehydrogenase kinase

ABSTRACT

The present invention provides methods and compositions for reducing lactate production and increasing polypeptide production in cultured cells. In one aspect, the invention provides a method comprising culturing cells expressing a) a small interfering RNA (siRNA) specific for a lactate dehydrogenase (LDH) and b) an siRNA specific for a pyruvate dehydrogenase kinase (PDHK). In another aspect, the invention provides cultured cells or vectors comprising an siRNA specific for a LDH and an siRNA specific for a PDHK.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/688,075, filed Nov. 28, 2012, which is a continuation ofInternational Patent Application No. PCT/US2011/038191, filed May 26,2011, which claims priority benefit to U.S. Provisional PatentApplication No. 61/349,727 filed May 28, 2010, the disclosures of whichare incorporated herein by reference in their entirety.

SEQUENCE LISTING

The content of the following submission on ASCII text file isincorporated herein by reference in its entirety: a computer readableform (CRF) of the Sequence Listing (file name:146392007810seqlisting.txt, date recorded: Sep. 14, 2016, size: 4 KB).

FIELD OF THE INVENTION

The field of this invention relates generally to methods andcompositions for reducing lactate production and increasing polypeptideproduction in cultured cells.

BACKGROUND OF THE INVENTION

Biopharmaceutical market is growing rapidly, and the industry isprojected to reach $70 billion dollars by year 2010. See GeneticEngineering in Livestock: New Applications and InterdisciplinaryPerspectives (Engelhard et al., 2009) Springer Berlin Heidelberg. Giventhe increase in demand in therapeutic proteins and the increase incompetitions in market sharing among companies, there is a need inimproving technologies to achieve better productivity in therapeuticproteins. Towards this goal, different approaches, such as host cellengineering, have been explored. See Kuystermans et al., Cytotechnology53(1-3):3-22 (2007); and O'Callaghan and James, Brief Funct. GenomicProteomic 7(2):95-110 (2008). Cultured cells, such as Chinese HamsterOvary (CHO) cells, are widely used to produce therapeutic proteins. Forexample, pH-controlled fed-batch bioreactor culture has been used widelyto produce recombinant monoclonal antibodies. Langheinrich and Nienow,Biotechnol. Bioeng. 66(3):171-9 (1999). Lactate is one of the mainaccumulated waste products during fed-batch culture, and it has beenshown to inhibit cell growth and protein production. See Glacken et al.,Biotechnol. Bioeng. 32:491-506 (1988); and Lao and Toth, Biotechnol.Prog. 13:688-691 (1997). This in turn leads to an increase in the amountof alkali needed for adding into the culture medium to control the pH.Dietl et al., J. Immunol. 184(3):1200-9 (2010): Langheinrich and Nienow,Biotechnol. Bioeng, 66(3):171-9 (1999). Increased addition of alkali tothe cell culture medium for maintaining the pH can result in an increasein osmolality, and this increase can lead to cell growth inhibition anddecreased antibody productivity. Cruz et al., Enzyme Microb. Technol.27(1-2):43-52 (2000); Iran et al., Biotechnol. Bioeng. 66:238-246(1999). Hence, reducing the lactate level is desired for the developmentof polypeptide or a higher titer antibody production process.

There are many factors that can influence lactate production in cellculture, such as controlling the pyruvate level. See Liu et al., J.Biol. Chem., 284(5):2811-22 (2009); and Samuvel et al., J. of Immunol.182(4):2476-84 (2009). Pyruvate is the substrate for the enzymespyruvate dehydrogenase (PDH) and lactate dehydrogenase (LDH).

The PDH complex is a multi-enzyme unit consisting of three catalyticenzymes, E1, E2, and E3. Patel and Korotchkina, Exp. Mol. Med.33(4):191-7 (2001). This complex catalyzes the rate-limiting conversionreaction in converting from pyruvate to acetyl-CoA, which is the entrypoint of tricarboxylic acid (TCA) cycle. The activity of PDH isregulated by the enzymes pyruvate dehydrogenase kinases (PDHK(s)) andpyruvate dehydrogenase phosphatases (PDHPs). PDHKs phosphorylate PDH tosuppress its enzymatic activity, whereas PDHP dephosphorylate and thusactivate PDH. See Patel and Korotchkina, Exp. Mol. Med. 33(4):191-7(2001); Roche and Hiromasa, Cell Mol. Life Sci. 64(7-8):830-49 (2007);Holness and Sugden, Biochemical Society Transactions, 31:1143-1151(2003). There are four isotypes of PDHK in mammalian cells (PDHK1,PDHK2, PDHK3, and PDHK4) with tissue specific distributions. See Harriset al., Adv. Enzyme Regul. 42:249-59 (2002); and Bowker-Kinley et al.,Biochem. J. 329(1):191-6 (1998).

LDH directly catalyzes the interconversion of pyruvate and lactate withconcurrent interconversion of NADH and NAD+. In mammalian cells, LDHsexist as either homo- or heterotetramers consisting mostly A and Bsubunits (or H and M subunits, respectively) encoded by LDHa and LDHbgenes, and sometimes homotetramers of C subunit encoded by LDHc genes.See Baumgart et al., J. Biol. Chem. 271(7):3846-55 (1996); Li et al., J.Biol. Chem. 258(11):7029-32 (1983); Skory C. D., Appl. Environ.Microbiol. 66(6):2343-8 (2000); and Read et al., Proteins 43(2):175-185(2001). For example, in CHO cells, LDH isotypes have been shown to beintermediates of the A3B and A2B2 tetramer. Jeong et al., Biochem.Biophys. Res. Commun. 289(5): 1141-9 (2001). Previous studies have shownthat down-regulating LDHa in CHO cells by disrupting the gene viahomologous recombination (Chen et al., Biotechnol. Bioeng. 72(1):55-61(2(2001)), antisense technology (Jeong et al., Biochem. Biophys. Res.Commun. 289(5):1141-9 (2001)), or small or short interfering RNA (siRNA)(Kim and Lee, Appl. Microbiol. Biotechnol. 74(1):152-9 (2007)) canreduce lactate level, but did not achieve appreciable improvement inprotein productivity. For example, in the case of LDHa specific siRNA,even though there was reportedly a 45-79% reduction in lactate level,there was no significant improvement in Specific Productivity (Qp) andproduct (antibody) titer, suggesting that knocking down LDHa alone inCHO cells is not sufficient to improve Qp and product yield efficiently.Thus, more efficient methods for reducing lactate production are neededfor achieving a better therapeutic polypeptide production.

All publications, patents, and patent applications cited herein arehereby incorporated by reference herein in their entirety for allpurposes to the same extent as if each individual publication, patent,and patent application were specifically and individually indicated tobe so incorporated by reference.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and compositions for reducinglactate production and increasing polypeptide production in culturedcells. The inventors have discovered that concomitant downregulation ofa LDH and PDHKs via siRNAs in cultured cells expressing polypeptides(e.g., antibodies) decreased lactate level, lactate production rate, andosmolality, and increased specific polypeptide productivity (e.g.,Specific Productivity) and polypeptide production (e.g., productivity).Further, these cultured cells with downregulated LDH and PDHKs exhibitedno negative impact on cell growth, cell viabilities, and the quality ofpolypeptides produced.

In one aspect, the invention provides a method for reducing lactateproduction in cultured cells, the method comprising culturing cellsexpressing a) a small interfering RNA (siRNA) specific for a lactatedehydrogenase (LDH) and b) an siRNA specific for a pyruvatedehydrogenase kinase (PDHK).

In another aspect, the invention provides cells in culture comprising a)an siRNA specific for a LDH and an siRNA specific for a PDHK.

In some embodiments, the cultured cells further express an siRNAspecific for a second PDHK. In some embodiments, the cultured cellsfurther express an siRNA specific for a third PDHK. In some embodiments,the cultured cells further express an siRNA specific for a fourth PDHK.

In another aspect, the invention provides a method for reducing lactateproduction in cultured cells, the method comprising culturing cellscomprising a first heterologous nucleic acid sequence encoding a smallinterfering RNA (siRNA) specific for a lactate dehydrogenase (LDH) and asecond heterologous nucleic acid sequence encoding an siRNA specific fora pyruvate dehydrogenase kinase (PDHK), wherein the first heterologousnucleic acid sequence is operably linked to a first promoter, andwherein the second heterologous nucleic acid sequence is operably linkedto a second promoter.

In another aspect, the invention provides cells in culture comprising afirst heterologous nucleic acid sequence encoding a first siRNA specificfor a LDH and a second heterologous nucleic acid sequence encoding asecond siRNA specific for a PDHK, wherein the first heterologous nucleicacid sequence is operably linked to a first promoter, and wherein thesecond heterologous nucleic acid sequence is operably linked to a secondpromoter.

In some embodiments, the cells further comprise a third heterologousnucleic acid sequence encoding an siRNA specific for a second PDHK andwherein the third heterologous nucleic acid sequence is operably linkedto a third promoter. In some embodiments, the cells further comprise afourth heterologous nucleic acid sequence encoding an siRNA specific fora third PDHK and wherein the fourth heterologous nucleic acid sequenceis operably linked to a fourth promoter. In some embodiments, the cellsfurther comprise a fifth heterologous nucleic acid sequence encoding ansiRNA specific for a fifth PDHK and wherein the fifth heterologousnucleic acid sequence is operably linked to a fifth promoter.

In some embodiments, the LDH is LDHa, LDHb, or LDHc.

In some embodiments, the PDHK is selected from the group consisting ofPDHK1, PDHK2, PDHK3, and PDHK4. In some embodiments, the PDHK isselected from the group consisting of PDHK1, PDHK2, and PDHK3. In someembodiments, the PDHK is selected from the group consisting of PDHK1 andPDHK2. In some embodiments, the PDHK is selected from the groupconsisting of PDHK1 and PDHK3. In some embodiments, the PDHK is selectedfrom the group consisting of PDHK2 and PDHK3.

In some embodiments, the method for reducing lactate production incultured cells comprises culturing cells comprising a first heterologousnucleic acid sequence encoding an siRNA specific for a lactatedehydrogenase (LDH) and a second, third, and fourth heterologous nucleicacid sequences encoding three different siRNAs specific for a first,second, and third PDHKs, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the second,third, and fourth heterologous nucleic acid sequences are operablylinked to a second, third, and fourth promoters, respectively. In someembodiments, the LDH is LDHa, wherein the first PDHK is PDHK1, thesecond PDHK is PDHK2, and the third PDHK is PDHK3.

In some embodiments, the cells in culture comprises a first heterologousnucleic acid sequence encoding a first siRNA specific for a LDH and asecond, third, and fourth heterologous nucleic acid sequences encodingthree different siRNAs specific for a first, second, and third PDHKs,wherein the first heterologous nucleic acid sequence is operably linkedto a first promoter, and wherein the second, third, and fourthheterologous nucleic acid sequences are operably linked to a second,third, and fourth promoters, respectively. In some embodiments, the LDHis LDHa, wherein the first PDHK is PDHK1, the second PDHK is PDHK2, andthe third PDHK is PDHK3.

In some embodiments, the cultured cells produce a heterologouspolypeptide. In some embodiments, the heterologous polypeptide is anantibody.

In some embodiments, the lactate synthesis rate of the cultured cells islower than the lactate consumption rate. In some embodiments, theaverage lactate production rate is less than about negative 0.02 mg/10⁶cells/day.

In some embodiments, the cultured cells containing siRNAs specific forthe LDH and PDHK(s) has an osmolality at less than about 300 mOsm.

In some embodiments, the cultured cells have a Specific Productivity(Qp) of at least about 75% higher than cultured cells without theheterologous nucleic acid sequence comprising the PDHK(s) and the LDH.

In some embodiments, the cultured cells have a Specific Productivity(Qp) of at least about 75% higher than cultured cells without the siRNAsspecific for the LDH and PDHK(s).

In some embodiments, the cultured cells have a polypeptide productivity(e.g., antibody productivity or titer in g/L) of about 10% to about 800%higher than cultured cells without the heterologous nucleic acidsequence comprising the PDHK(s) and the LDH. In some embodiments, thecultured cells have a polypeptide productivity of about 55% higher thancultured cells without the heterologous nucleic acid sequence comprisingthe PDHK(s) and the LDH. In some embodiments, the cultured cells have ofa polypeptide productivity of at least about 68% higher than culturedcells without the heterologous nucleic acid sequence comprising thePDHK(s) and the LDH.

In some embodiments, the cultured cells have a polypeptide productivityof about 10% to about 8(00% higher than cultured cells without thesiRNAs specific for the PDHK(s) and the LDH. In some embodiments, thecultured cells have a polypeptide productivity of about 55% higher thancultured cells without the siRNAs specific for the PDHK(s) and the LDH.In some embodiments, the cultured cells have a polypeptide productivityof at least about 68% higher than cultured cells without the siRNAsspecific for the PDHK(s) and the LDH.

In some embodiments, the cultured cells are mammalian cells. In someembodiments, the cultured cells are non-mammalian cells.

In another aspect, the invention provides a method of silencing ordown-regulating LDH and PDHK transcription in a cultured cellcomprising: introducing into the cell a vector comprising a firstheterologous nucleic acid sequence encoding a siRNA specific for the LDHand a second heterologous nucleic acid sequence encoding an siRNAspecific for the PDHK, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the secondheterologous nucleic acid sequence is operably linked to a secondpromoter, wherein the siRNAs are expressed, thereby silencing ordown-regulating gene transcription of the LDH and the PDHK.

In another aspect, the invention provides a method of making a cell thatexhibits decreased lactate production in culture, comprising introducinginto the cell a vector comprising a first heterologous nucleic acidsequence encoding a siRNA specific for the LDH and a second heterologousnucleic acid sequence encoding an siRNA specific for the PDHK, whereinthe first heterologous nucleic acid sequence is operably linked to afirst promoter, and wherein the second heterologous nucleic acidsequence is operably linked to a second promoter.

In another aspect, the invention provides a vector comprising a firstheterologous nucleic acid sequence encoding a small interfering RNA(siRNA) specific for a lactate dehydrogenase (LDH) and a secondheterologous nucleic acid sequence encoding an siRNA specific for apyruvate dehydrogenase kinase (PDHK), wherein the first heterologousnucleic acid sequence is operably linked to a first promoter, andwherein the second heterologous nucleic acid sequence is operably linkedto a second promoter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows siRNA construct targeting LDHa/PDHK1, 2, 3. siRNAstargeting LDHa, PDHK1, PDHK2 and PDHK3 were cloned into single pSilencer3.1 hygromycin vector. Targeting sequence for LDHa was under U6 promoterregulation whereas siRNAs for PDHK1, 2, and 3 were under H1 promoterregulation.

FIG. 2 shows relative LDHa, PDHK1, 2, and 3 mRNA expression levels inselected 12 siRNA clones (as shown in light gray color). Expressionlevels of LDHa and PDHKs were normalized to housekeeping geneb-microglobulin. The average mRNA expression levels from 12 mock cloneswere shown in dark gray color.

FIGS. 3A-3C show lactate profiles, average lactate production rates, andday 14 pH values in fed-batch shake flask evaluation. Lactateconcentrations were measured using Nova analyzer on day 3, 7, 10 and 14during a 14-day shake flask evaluation. FIG. 3A). Lactate profile ofmock (dark gray) and siRNA (light gray) clones; FIG. 3B). Averagelactate production rate between days 3 and 14 (mg/106 cells/day); andFIG. 3C). Day 14 pH values. The fed-batch shake flask experiments wereperformed 3 times and the data shown is from 1 experiment.

FIGS. 4A-4C show titer. Specific Productivity (Qp) and cell growthprofiles in fed-batch shake flask evaluation. FIG. 4A). Day 14titer(productivity) in g/L; FIG. 4B). Specific Productivity in pg/cell/day;and FIG. 4C). Cell growth measure by integrated viable cell count (IVCC)in 100 millions of cells per day per liter. Mock clones are in dark grayand siRNA clones are in light gray.

FIGS. 5A-5C lactate profile, average lactate production rates, andosmolality profile in 2 L bioreactor evaluations. FIG. 5A). Lactateprofile; FIG. 5B). Average lactate production rates; and FIG. 5C).Osmolality profile.

FIG. 6 shows productivity profile of cultured cells containing siRNA,mock, or parent clones in 2 L bioreactor evaluation.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides methods and compositions for reducinglactate production and increasing polypeptide production in culturedcells. The inventors have discovered that concomitant downregulation ofa LDH and PDHKs via siRNAs by a process known as RNA interference (RNAi)in cultured cells expressing polypeptides (e.g., antibodies) decreasedlactate level, lactate production rate, and cell osmolality, andincreased specific polypeptide productivity (e.g., SpecificProductivity) and polypeptide production (e.g., productivity). Further,these cultured cells with the downregulated LDH and PDHKs exhibited nonegative impact on cell growth, cell viabilities, and the quality ofpolypeptides produced. Thus, without wishing to be bound by theory,decreasing the pyruvate-lactate conversion by knocking down theexpression of a LDH and promoting pyruvate into tricarboxylic acid cycle(TCA or Krebs cycle) by knocking down the expression of one or morePDHKs may create a synergistic effect in lactate reduction and providingcells with more energy and metabolic intermediates. These effects inturn may lead to increased polypeptide (e.g., antibody) production incultured cells.

Accordingly, in one aspect of the invention, provided is a method forreducing lactate production in cultured cells, comprising culturingcells expressing a) an siRNA specific for a LDH and b) an siRNA specificfor a PDHK.

In another aspect, provided are cells in culture comprising a) an si RNAspecific for a LDH and an siRNA specific for a PDHK.

In another aspect, the invention provides a method for reducing lactateproduction in cultured cells, comprising culturing cells comprising afirst heterologous nucleic acid sequence encoding an siRNA specific fora LDH and a second heterologous nucleic acid sequence encoding an siRNAspecific for a PDHK, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the secondheterologous nucleic acid sequence is operably linked to a secondpromoter.

In yet another aspect, the invention provides cells in culturecomprising a first heterologous nucleic acid sequence encoding a firstsiRNA specific for a LDH and a second heterologous nucleic acid sequenceencoding a second siRNA specific for a PDHK, wherein the firstheterologous nucleic acid sequence is operably linked to a firstpromoter, and wherein the second heterologous nucleic acid sequence isoperably linked to a second promoter.

The practice of the present invention will employ, unless otherwiseindicated, conventional techniques of molecular biology (includingrecombinant techniques), microbiology, cell biology, biochemistry andimmunology, which are within the skill of the art. Such techniques areexplained fully in the literature, such as, Molecular Cloning: ALaboratory Manual, second edition (Sambrook et al., 1989) Cold SpringHarbor Press; Oligonucleotide Synthesis (M. J. Gait, ed., 1984); Methodsin Molecular Biology, Humana Press; Cell Biology: A Laboratory Notebook(J. E. Cellis, ed., 1998) Academic Press; Animal Cell Culture (R. I.Freshney, ed., 1987); Introduction to Cell and Tissue Culture (J. P.Mather and P. E. Roberts, 1998) Plenum Press; Cell and Tissue Culture:Laboratory Procedures (A. Doyle, J. B. Griffiths, and D. G. Newell,eds., 1993-1998) J. Wiley and Sons; Methods in Enzymology (AcademicPress, Inc.); Handbook of Experimental Immunology (D. M. Weir and C. C.Blackwell, eds.); Gene Transfer Vectors for Mammalian Cells (J. M.Miller and M. P. Calos, eds., 1987); Current Protocols in MolecularBiology (F. M. Ausubel et al., eds., 1987); PCR: The Polymerase ChainReaction, (Mullis et al., eds., 1994); Current Protocols in Immunology(J. E. Coligan et al., eds., 1991); Short Protocols in Molecular Biology(Wiley and Sons, 1999); Immunobiology (C. A. Janeway and P. Travers,1997); Antibodies (P. Finch, 1997): Antibodies: a practical approach (D.Catty., ed., IRL Press, 1988-1989); Monoclonal antibodies: a practicalapproach (P. Shepherd and C. Dean, eds., Oxford University Press, 2000);Using antibodies: a laboratory manual (E. Harlow and D. Lane (ColdSpring Harbor Laboratory Press, 1999); The Antibodies (M. Zanetti and J.D. Capra, eds., Harwood Academic Publishers, 1995).

Definitions

As used herein, the term “cells in culture” or “cultured cells” referstwo or more cells in a solution (e.g., a cell medium) that allows thecells to undergo one or more cell divisions.

The term “polynucleotide” or “nucleic acid,” as used interchangeablyherein, refers to polymers of nucleotides of any length, and include DNAand RNA. The nucleotides can be deoxyribonucleotides, ribonucleotides,modified nucleotides or bases, and/or their analogs, or any substratethat can be incorporated into a polymer by DNA or RNA polymerase. Apolynucleotide may comprise modified nucleotides, such as methylatednucleotides and their analogs. If present, modification to thenucleotide structure may be imparted before or after assembly of thepolymer. The sequence of nucleotides may be interrupted bynon-nucleotide components. A polynucleotide may be further modifiedafter polymerization, such as by conjugation with a labeling component.Other types of modifications include, for example, “caps”, substitutionof one or more of the naturally occurring nucleotides with an analog,internucleotide modifications such as, for example, those with unchargedlinkages (e.g., methyl phosphonates, phosphotriesters, phosphoamidates,cabamates, etc.) and with charged linkages (e.g., phosphorothioates,phosphorodithioates, etc.), those containing pendant moieties, such as,for example, proteins (e.g., nucleases, toxins, antibodies, signalpeptides, ply-L-lysine, etc.), those with intercalators (e.g., acridine,psoralen, etc.), those containing chelators (e.g., metals, radioactivemetals, boron, oxidative metals, etc.), those containing alkylators,those with modified linkages (e.g., alpha anomeric nucleic acids, etc.),as well as unmodified forms of the polynucleotide(s). Further, any ofthe hydroxyl groups ordinarily present in the sugars may be replaced,for example, by phosphonate groups, phosphate groups, protected bystandard protecting groups, or activated to prepare additional linkagesto additional nucleotides, or may be conjugated to solid supports. The5′ and 3′ terminal OH can be phosphorylated or substituted with aminesor organic capping group moieties of from 1 to 20 carbon atoms. Otherhydroxyls may also be derivatized to standard protecting groups.Polynucleotides can also contain analogous forms of ribose ordeoxyribose sugars that are generally known in the art, including, forexample, 2′-O-methyl-, 2′-O-allyl, 2′-fluoro- or 2′-azido-ribose,carbocyclic sugar analogs, anomeric sugars, epimeric sugars such asarabinose, xyloses or lyxoses, pyranose sugars, furanose sugars,sedoheptuloses, acyclic analogs and abasic nucleoside analogs such asmethyl riboside. One or more phosphodiester linkages may be replaced byalternative linking groups. These alternative linking groups include,but are not limited to, embodiments wherein phosphate is replaced byP(O)S(“thioate”), P(S)S (“dithioate”). “(O)NR₂ (“amidate”), P(O)R,P(O)OR′, CO or CH₂ (“formacetal”), in which each R or R′ isindependently H or substituted or unsubstituted alkyl (1-20 C)optionally containing an ether (—O—) linkage, aryl, alkenyl, cycloalkyl,cycloalkenyl or araldyl. Not all linkages in a polynucleotide need beidentical. The preceding description applies to all polynucleotidesreferred to herein, including RNA and DNA.

The term “RNA interference (RNAi)” refers to the process ofsequence-specific, transcriptional gene silencing (e.g.,posttranscriptional gene silencing) mediated or initiated by siRNA.Without wishing to be bound by theory, during RNAi, in practicing themethods of the invention, siRNA can induce degradation of target mRNAwith consequent sequence-specific inhibition of gene expression of a LDHand one or more PDHKs.

The term “heterologous nucleic acid” or “heterologous polypeptide”refers to a nucleic acid or a polypeptide whose sequence is notidentical to that of another nucleic acid or polypeptide naturally foundin the same host cell.

The term “small interfering RNA,” “short interfering RNA,” or “siRNA”refers to an RNA duplex of nucleotides, or, in some alternative aspects,a single molecule of RNA that is targeted to a nucleic acid of interest,e.g., a LDH or PDHK(s). The siRNA comprise a sense RNA strand and acomplementary antisense RNA strand annealed together by standardWatson-Crick base-pairing interactions. SiRNA can either be transfecteddirectly or otherwise produced within a cultured cell.

In one variation, the sense RNA strand and the complementary antisenseRNA strand are linked by a spacer leading to the expression of astem-loop or a hairpin structure termed short hairpin RNA (shRNA). Thehairpin is then cleaved by an endonuclease (e.g., Dicer) to generate ansiRNA. In another variation, the shRNA is a bi-functional shRNAconsisting of two stem-loop structures, with one stem-loop structurecomposed of fully matched sequence guiding the RNA duplex for mRNAdegradation via cleavage dependent RISC (RNA-induced silencing complex)loading, and with the second stein-loop structure composed ofmis-matched strand inhibiting translation of the mRNA through mRNAsequestration via cleavage-independent RISC loading.

As used herein, an siRNA “specific” for a LDH or PDHK refers to an siRNAthat is targeted to a nucleic acid of interest (e.g., a LDH or PDHK(s))and that the nucleotide sequence of the duplex portion of the siRNA iscomplementary to a nucleotide sequence of the targeted gene (e.g., a LDHor PDHK(s)).

As used herein, “operably linked” as used herein refers to a functionalrelationship between two or more nucleic acid (e.g., DNA) segments.Typically, it refers to the functional relationship of transcriptionalregulatory sequence to a transcribed sequence. For example, a promoteris operably linked to a coding sequence, such as a nucleic acid of theinvention, if it stimulates or modulates the transcription of the codingsequence in an appropriate host cell or other expression system.Generally, promoter transcriptional regulatory sequences that areoperably linked to a transcribed sequence are physically contiguous tothe transcribed sequence, i.e., they are cis-acting. However, sometranscriptional regulatory sequences, such as enhancers, need not bephysically contiguous or located in close proximity to the codingsequences whose transcription they enhance.

As used herein, the term “promoter” includes all sequences capable ofdriving transcription of a coding sequence in a cultured cell, e.g., amammalian cell. Thus, promoters used in the constructs of the inventioninclude cis-acting transcriptional control elements and regulatorysequences that are involved in regulating or modulating the timingand/or rate of transcription of a gene (e.g., a LDH or PDHK(s)). Forexample, a promoter can be a cis-acting transcriptional control element,including an enhancer, a promoter, a transcription terminator, an originof replication, a chromosomal integration sequence, 5′ and 3′untranslated regions, or an intronic sequence, which are involved intranscriptional regulation. These cis-acting sequences typicallyinteract with proteins or other biomolecules to carry out (turn on/off,regulate, modulate, etc.) transcription. “Constitutive” promoters arethose that drive expression continuously under most environmentalconditions and states of development or cell differentiation.“Inducible” or “regulatable” promoters direct expression of the nucleicacid of the invention under the influence of environmental conditions ordevelopmental conditions. Examples of environmental conditions that mayaffect transcription by inducible promoters include anaerobicconditions, elevated temperature, drought, or the presence of light.

As used herein, “vector” means a construct, which is capable ofdelivering, and preferably expressing, one or more gene(s) orsequence(s) of interest (e.g., LDHa and PDHK(s)) in a host cell.Examples of vectors include, but are not limited to, viral vectors,naked DNA or RNA expression vectors, plasmid, cosmid or phage vectors,DNA or RNA expression vectors associated with cationic condensingagents, DNA or RNA expression vectors encapsulated in liposomes, andcertain eukaryotic cells, such as producer cells. Suitable vectors arethose which are compatible with the host cell employed. Suitable vectorscan be derived, for example, from a bacterium, a virus (such asbacteriophage T7 or a M-13 derived phage), a cosmid, a yeast, or aplant. Protocols for obtaining and using such vectors are known to thosein the art (see, for example. Sambrook et al., Molecular Cloning: ALaboratory Manual, 2^(nd) ed., Cold Spring Harbor, 1989).

As used herein, the average lactate production rate is calculated aslactate synthesis rate minus lactate consumption rate in mg/cells/day.

As used herein, “Specific Productivity” or “Qp” refers to the specificprotein, e.g., antibody, production rate in pg/cell/day. Specificproductivity is calculated as protein titer (pg/cell/day)/IVCC(calculate integrated viable cell count; cell/day).

The terms “polypeptide” and “protein” are used interchangeably herein torefer to polymers of amino acids of any length. The polymer may belinear or branched, it may comprise modified amino acids, and it may beinterrupted by non-amino acids. The terms also encompass an amino acidpolymer that has been modified naturally or by intervention; forexample, disulfide bond formation, glycosylation, lipidation,acetylation, phosphorylation, or any other manipulation or modification,such as conjugation with a labeling component. Also included within thedefinition are, for example, polypeptides containing one or more analogsof an amino acid (including, for example, unnatural amino acids, etc.),as well as other modifications known in the art.

The term “antibody” is used in the broadest sense and specificallycovers monoclonal antibodies (including full length monoclonalantibodies), polyclonal antibodies, multispecific antibodies (e.g.,bispecific antibodies), and antibody fragments.

“Antibody fragments” comprise a portion of a full length antibody,generally the antigen binding or variable region thereof. Examples ofantibody fragments include Fab, Fab′, F(ab′)₂, and Fv fragments;single-chain antibody molecules; diabodies; linear antibodies; andmultispecific antibodies formed from antibody fragments.

The term “monoclonal antibody” as used herein refers to an antibodyobtained from a population of substantially homogeneous antibodies,i.e., the individual antibodies comprising the population are identicalexcept for possible naturally occurring mutations that may be present inminor amounts. Monoclonal antibodies are highly specific, being directedagainst a single antigenic site. Furthermore, in contrast toconventional (polyclonal) antibody preparations which typically includedifferent antibodies directed against different determinants (epitopes),each monoclonal antibody is directed against a single determinant on theantigen. The modifier “monoclonal” indicates the character of theantibody as being obtained from a substantially homogeneous populationof antibodies, and is not to be construed as requiring production of theantibody by any particular method. For example, the monoclonalantibodies to be used in accordance with the present invention may bemade by the hybridoma method first described by Kohler et al, Nature256:495 (1975), or may be made by recombinant DNA methods (see, e.g.,U.S. Pat. No. 4,816,567). The “monoclonal antibodies” may also beisolated from phage antibody libraries using the techniques described inClackson et al., Nature 352:624-628 (1991) and Marks et al., J. Mol.Biol. 222:581-597 (1991), for example.

The monoclonal antibodies herein specifically include “chimeric”antibodies (immunoglobulins) in which a portion of the heavy and/orlight chain is identical with or homologous to corresponding sequencesin antibodies derived from a particular species or belonging to aparticular antibody class or subclass, while the remainder of thechain(s) is identical with or homologous to corresponding sequences inantibodies derived from another species or belonging to another antibodyclass or subclass, as well as fragments of such antibodies, so long asthey exhibit the desired biological activity (U.S. Pat. No. 4,816,567;and Morrison et al., Proc. Natl. Acad. Sci. USA 81:6851-6855 (1984)).

The term “hypervariable region” when used herein refers to the aminoacid residues of an antibody which are responsible for antigen-binding.The hypervariable region comprises amino acid residues from a“complementarity determining region” or “(CDR” (i.e. residues 24-34(L1), 50-56 (L2) and 89-97 (L3) in the light chain variable domain and31-35 (H1), 50-65 (H2) and 95-102 (H3) in the heavy chain variabledomain; Kabat et al., Sequences of Proteins of Immunological Interest,5th Ed. Public Health Service. National Institutes of Health, Bethesda,Md. (1991)) and/or those residues from a “hypervariable loop” (i.e.residues 26-32 (L1), 50-52 (L2) and 91-96 (L3) in the light chainvariable domain and 26-32 (H1), 53-55 (H2) and 96-101 (H3) in the heavychain variable domain; Chothia and Lesk J. Mol. Biol. 196:901-917(1987)). “Framework” or “FR” residues are those variable domain residuesother than the hypervariable region residues as herein defined.

“Humanized” forms of non-human (e.g., murine) antibodies are chimericantibodies which contain minimal sequence derived from non-humanimmunoglobulin. For the most part, humanized antibodies are humanimmunoglobulins (recipient antibody) in which hypervariable regionresidues of the recipient are replaced by hypervariable region residuesfrom a non-human species (donor antibody) such as mouse, rat, rabbit ornonhuman primate having the desired specificity, affinity, and capacity.In some instances, Fv framework region (FR) residues of the humanimmunoglobulin are replaced by corresponding non-human residues.Furthermore, humanized antibodies may comprise residues which are notfound in the recipient antibody or in the donor antibody. Thesemodifications are made to further refine antibody performance. Ingeneral, the humanized antibody will comprise substantially all of atleast one, and typically two, variable domains, in which all orsubstantially all of the hypervariable loops correspond to those of anon-human immunoglobulin and all or substantially all of the FR regionsare those of a human immunoglobulin sequence. The humanized antibodyoptionally also will comprise at least a portion of an immunoglobulinconstant region (Fc), typically that of a human immunoglobulin. Forfurther details, see Jones et al., Nature 321:522-525 (1986); Riechmannet al., Nature 332:323-329 (1988); and Presta, Curr. Op. Struct. Biol.2:593-596 (1992).

As used herein, the term “immunoadhesin” designates antibody-likemolecules which combine the “binding domain” of a heterologous “adhesin”protein (e.g. a receptor, ligand or enzyme) with the effector functionsof an immunoglobulin constant domain. Structurally, the immunoadhesinscomprise a fusion of the adhesin amino acid sequence with the desiredbinding specificity which is other than the antigen recognition andbinding site (antigen combining site) of an antibody (i.e. is“heterologous”) and an immunoglobulin constant domain sequence. Theimmunoglobulin constant domain sequence in the immunoadhesin ispreferably derived from γ1, γ2, or γ4 heavy chains since immunoadhesinscomprising these regions can be purified by Protein A chromatography(Lindmark et al., J. Immunol. Meth. 62:1-13 (1983)).

The term “ligand binding domain” as used herein refers to any nativecell-surface receptor or any region or derivative thereof retaining atleast a qualitative ligand binding of a corresponding native receptor.In a specific embodiment, the receptor is from a cell-surfacepolypeptide having an extracellular domain which is homologous to amember of the immunoglobulin supergenefamily. Other receptors, which arenot members of the immunoglobulin supergenefamily but are nonethelessspecifically covered by this definition, are receptors for cytokines,and in particular receptors with tyrosine kinase activity (receptortyrosine kinases), members of the hematopoietin and nerve growth factorreceptor superfamilies, and cell adhesion molecules, e.g. (E-, L- andP-) selectins.

The term “receptor binding domain” is used to designate any nativeligand for a receptor, including cell adhesion molecules, or any regionor derivative of such native ligand retaining at least a qualitativereceptor binding ability of a corresponding native ligand. Thisdefinition, among others, specifically includes binding sequences fromligands for the above-mentioned receptors.

An “antibody-immunoadhesin chimera” comprises a molecule which combinesat least one binding domain of an antibody (as herein defined) with atleast one immunoadhesin (as defined in this application). Exemplaryantibody-immunoadhesin chimeras are the bispecific CD4-IgG chimerasdescribed in Berg et al., PNAS (USA) 88:4723-4727 (1991) and Chamow etal., J. Immunol. 153:4268 (1994).

The term “osmolality” refers to the number of solute particles dissolvedin 1 liter of solution. Solutes which can be added to the culture mediumso as to increase the osmolality thereof include proteins, peptides,amino acids, non-metabolized polymers, vitamins, ions, salts (e.g.,sodium or potassium salts), sugars, metabolites, organic acids, lipids,etc. When used herein, the abbreviation “mOsm” means “milliosmoles/LiterH₂O.”

As used herein, a “host cell” includes an individual cell, culturedcells, or cell in culture that can be or has been a recipient forvector(s) or siRNA(s) for incorporation of polynucleotide inserts toproduce polypeptide. Host cells include progeny of a single culturedcell, and the progeny may not necessarily be completely identical (inmorphology or in genomic DNA complement) to the original parent cell dueto natural, accidental, or deliberate mutation.

For use herein, unless clearly indicated otherwise, use of the terms“a”, “an,” and the like refers to one or more.

Reference to “about” a value or parameter herein includes (anddescribes) embodiments that are directed to that value or parameter perse. For example, description referring to “about X” includes descriptionof “X.” Numeric ranges are inclusive of the numbers defining the range.

It is understood that wherever embodiments are described herein with thelanguage “comprising,” otherwise analogous embodiments described interms of “consisting of” and/or “consisting essentially of” are alsoprovided.

Where aspects or embodiments of the invention are described in terms ofa Markush group or other grouping of alternatives, the present inventionencompasses not only the entire group listed as a whole, but each memberof the group individually and all possible subgroups of the main group,but also the main group absent one or more of the group members. Thepresent invention also envisages the explicit exclusion of one or moreof any of the group members in the claimed invention.

Methods for Reducing Lactate Production

The methods herein involve culturing cells expressing siRNAs specificfor a LDH and at least one or more PDHKs to reduce lactate productionvia RNA interference (RNAi). In one aspect, the method comprisesculturing cells expressing a) an siRNA specific for LDH and b) an siRNAspecific for a PDHK.

In some embodiments, the cultured cells further express an siRNAspecific for a second PDHK. In some embodiments, the cultured cellsfurther express an siRNA specific for a third PDHK. In some embodiments,the cultured cells further express an siRNA specific for a fourth PDHK.

In another aspect, the method comprises a first heterologous nucleicacid sequence encoding an siRNA specific for a LDH and a secondheterologous nucleic acid sequence encoding an siRNA specific for aPDHK, wherein the first heterologous nucleic acid sequence is operablylinked to a first promoter, and wherein the second heterologous nucleicacid sequence is operably linked to a second promoter.

In another aspect, provided is a method of silencing or down-regulatingLDH and PDHK transcription in a cultured cell comprising: introducinginto the cell a vector comprising a first heterologous nucleic acidsequence encoding an siRNA specific for the LDH and a secondheterologous nucleic acid sequence encoding an siRNA specific for thePDHK, wherein the first heterologous nucleic acid sequence is operablylinked to a first promoter, and wherein the second heterologous nucleicacid sequence is operably linked to a second promoter, wherein thesiRNAs are expressed, thereby silencing or down-regulating genetranscription of the LDH and the PDHK.

In some embodiments, the cultured cells further comprise a thirdheterologous nucleic acid sequence encoding an siRNA specific for asecond PDHK and wherein the third heterologous nucleic acid sequence isoperably linked to a third promoter. In some embodiments, the culturedcells further comprise a fourth heterologous nucleic acid sequenceencoding an siRNA specific for a third PDHK and wherein the fourthheterologous nucleic acid sequence is operably linked to a fourthpromoter. In some embodiments, the cultured cells further comprise afifth heterologous nucleic acid sequence encoding an siRNA specific fora fifth PDHK and wherein the fifth heterologous nucleic acid sequence isoperably linked to a fifth promoter.

In some embodiments, the LDH is LDHa, LDHb, or LDHc. In someembodiments, the PDHK is selected from the group consisting of PDHK1,PDHK2, PDHK3, and PDHK4. In some embodiments, the PDHK is selected fromthe group consisting of PDHK1, PDHK2, and PDHK3. In some embodiments,the PDHK is selected from the group consisting of PDHK2, PDHK3, andPDHK4. In some embodiments, the PDHK is selected from the groupconsisting of PDHK1, PDHK3, and PDHK4. In some embodiments, the PDHK isselected from the group consisting of PDHK1 and PDHK2. In someembodiments, the PDHK is selected from the group consisting of PDHK1 andPDHK3. In some embodiments, the PDHK is selected from the groupconsisting of PDHK2 and PDHK3. In some embodiments, the PDHK is selectedfrom the group consisting of PDHK2 and PDHK4. In some embodiments, thePDHK is selected from the group consisting of PDHK3 and PDHK4.

In some embodiments, the method comprises culturing cells expressing a)an siRNA specific for LDHa and b) an siRNA specific for PDHK1, PDHK2,and PDHK3, respectively. In some embodiments, the method comprisesculturing cells expressing a) an siRNA specific for LDHb and b) an siRNAspecific for PDHK1, PDHK2, and PDHK3, respectively. In some embodiments,the method comprises culturing cells expressing a) an siRNA specific forLDHc and b) an siRNA specific for PDHK1, PDHK2, and PDHK3, respectively.

In some embodiments, the method comprises culturing cells expressing a)an siRNA specific for LDHa, LDHb, or LDHc and b) an siRNA specific fortwo PDHKs, wherein the PDHK is selected from the group consisting ofPDHK1, PDHK2, PDHK3, and PDHK4. For example, the method comprisesculturing cells expressing a) an siRNA specific for LDHa and b) an siRNAspecific for PDHK1 and PDHK2, respectively.

In some embodiments, the mRNA expression level for a LDH is reduced byat least about 75% and the mRNA expression level for a PDHK is reducedby at least about 25% in cultured cells expressing a) an siRNA specificfor a LDH and b) an siRNA specific for a PDHK in comparison to culturedcells without the siRNAs specific for a LDH and a PDHK. In someembodiments, the LDH is LDHa, LDHb, or LDHc and the mRNA expressionlevel for the LDH is reduced by at least about 75%, at least about 80%,at least about 85%, at least about 90%, or at least about 95%. In someembodiments, the PDHK is PDHK1, PDHK2, or PDHK3, and the mRNA expressionlevel for the PDHK is reduced by at least about 25%, at least about 30%,at least about 35%, at least about 40%, at least about 45%, at leastabout 50%, at least about 55%, at least about 60%, at least about 65%,at least about 70%, at least about 75%, at least about 80%, at leastabout 85%, at least about 90%, or at least about 95%.

In some embodiments, in cultured cells expressing a) an siRNA specificfor LDHa and b) an siRNA specific for PDHK1, PDHK2, and PDHK3, the mRNAexpression level for LDHa is reduced by about 90% and the mRNAexpression levels for PDHK1, PDHK2, and PDHK3 are reduced by about 32%,83%, and 70%, respectively, in comparison to cultured cells without thesiRNAs specific for the LDHa, PDHK1, PDHK2, and PDHK3.

In some embodiments, the method comprises a first heterologous nucleicacid sequence encoding an siRNA specific for LDHa, LDHb, or LDHc, asecond heterologous nucleic acid sequence encoding an siRNA specific forPDHK1, a third heterologous nucleic acid sequence encoding an siRNAspecific for PDHK2, and a fourth heterologous nucleic acid sequenceencoding an siRNA specific for PDHK3, wherein the first heterologousnucleic acid sequence is operably linked to a first promoter, andwherein the second, third, and fourth heterologous nucleic acid sequenceis operably linked to a second promoter.

In some embodiments, the method comprises a first heterologous nucleicacid sequence encoding an siRNA specific for LDHa, LDHb, or LDHc, asecond heterologous nucleic acid sequence encoding an siRNA specific fora PDHK, and a third heterologous nucleic acid sequence encoding an siRNAspecific for a PDHK, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, wherein the second andthird heterologous nucleic acid sequences are operably linked to asecond promoter, and wherein the PDHK is selected from the groupconsisting of PDHK1. PDHK2, PDHK3, and PDHK4.

In some embodiments, the mRNA expression level for a LDH is reduced byat least about 75% and the mRNA expression level for a PDHK is reducedby at least about 25% in cultured cells comprising a first heterologousnucleic acid sequence encoding an siRNA specific for a LDH and a secondheterologous nucleic acid sequence encoding an siRNA specific for a PDHKin comparison to cultured cells without the heterologous nucleic acidsequence comprising the LDH and the PDHK(s), wherein the firstheterologous nuclei acid sequence is operably linked to a firstpromoter, and wherein the second heterologous nucleic acid sequence isoperably linked to a second promoter. In some embodiments, the LDH isLDHa, LDHb, or LDHc and the mRNA expression level for the LDH is reducedby at least about 75%, at least about 80%, at least about 85%, at leastabout 90%, or at least about 95%. In some embodiments, the PDHK isPDHK1, PDHK2, or PDHK3, and the mRNA expression level for the PDHK isreduced by at least about 25%, at least about 30%, at least about 35%,at least about 40%, at least about 45%, at least about 50%, at leastabout 55%, at least about 60%, at least about 65%, at least about 70%,at least about 75%, at least about 80%, at least about 85%, at leastabout 90%, or at least about 95%.

In some embodiments, in cultured cells comprising a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the second,third, and fourth heterologous nucleic acid sequence is operably linkedto a second promoter, the mRNA expression level for LDHa is reduced byabout 90% and the mRNA expression levels for PDHK1, PDHK2, and PDHK3 arereduced by about 32%, 83%, and 70%, respectively, in comparison tocultured cells without the siRNAs specific for the LDHa, PDHK1, PDHK2,and PDHK3.

The siRNA used in the invention described herein can be obtained or madefrom a variety of sources, e.g., produced in vitro, ex vivo or in vivo,as described herein. In some embodiments, the siRNA can contain fromabout 1 to about 200 nucleotides, from about 5 to about 100 nucleotides,from about 10 to about 50 nucleotides, from about 15 to about 30nucleotides, or from about 19 to about 25 nucleotides. In someembodiments, the length of the siRNA is less than 30 nucleotides. Insome embodiments, the length of the siRNAs is more than 30 nucleotides.In some embodiments, the siRNA can be 40, 39, 38, 37, 36, 35, 34, 33,32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15,14, 13, 12, 11, 10, 9 or less nucleotides in length.

In some embodiments, the siRNA can be generated by chemical synthesis,by in vitro transcription using a polymerase, or by an endoribonuclease(e.g., Dicer) digestion of long double strand RNA (dsRNA). In someembodiments, the siRNA can be entirely, or in part, comprised ofsynthetic nucleotides, natural bases or modified bases.

In some embodiments, the siRNA can be expressed intracellularly. ThesiRNA can be encoded by a nucleic acid sequence, and the nucleic acidsequence can also include one or more promoters. The nucleic acidsequence can also include a polyadenylation signal. In some embodiments,sense and antisense strands of the RNA duplex can be produced from twoindependent promoters and annealed with the cultured cell. In someembodiments, the sense and antisense strands of the RNA duplex can alsobe linked by a base pair spacer (e.g., a base pair spacer may comprise asingle or multiple base pair) or a stem-loop to form a shRNA andexpressed by a single promoter. In some embodiments, the shRNA can be abi-functional shRNA. The hairpin can be cleaved by an endoribonuclease(e.g., Dicer) to generate effective siRNA molecules. The spacer orstem-loop is positioned between the sense and antisense strands thatform the duplex. The stem-loop can vary in length. In some embodiments,the stem-loop is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 ormore nucleotides in length. The hairpin structure can also contain 3′ or5′ overhang portions. In some embodiments, the overhang is a 3′ or a 5′overhang 1, 2, 3, 4 or 5 nucleotides in length. Compositions and methodsfor RNA-mediated gene regulation by siRNA, shRNA, or bifunctional shRNAare described, for example, in U.S. Appl. No. 20090215860, Rutz andScheffold, Arthritis Research & Therapy, 6(2):78-85 (2004), and Rao etal., Advanced Drug Delivery Reviews 61:746-759 (2009).

In some embodiments, the siRNA used in the present invention can haveperfect homology with target sequences to produce target specificresponses. In some embodiments, the siRNA used in the present inventionhave about any of 99%, 98%, 97%, 96%, 95%, 94%, 92%, 91%, 90%, 88%, 86%,84%, 82%, 80%, 78%, 76%, 74%, 72%, 70%, 65%, 60%, 55%, 50%, 45%, 40%,35%, 30%, 25%, 20%, 15%, 10%, or 5%, homology with target sequences. Inone variation, the siRNA used in the present invention can hybridizeunder physiologic conditions to a nucleic acid target sequence, e.g., itcan specifically hybridize to a target sequence in a cell. e.g., invivo. In another variation, the siRNA targets more than one targetsequence, target marker or reporter gene.

The extent of sequence identity (homology) necessary for in vivotargeting of an siRNA to a target nucleic acid (e.g., specific bindingof an siRNA to a target sequence in a cell under physiologic conditions)can be tested under routine screening conditions, e.g., in cell cultureand the like.

In some embodiments, the target sequence for PDHK1 isGCAGTTCCTGGACTTCGGA (SEQ ID NO:2). In some embodiments, the targetsequence for PDHK2 is CATTCAGTACTTCTTGGAC (SEQ ID NO:3). In someembodiments, the target sequence for PDHK3 is TGTAGCTGATGTCGTGAAA (SEQID NO:4).

Lactate dehydrogenase (LDH) converts pyruvate into lactate. Theaccession numbers of exemplary LDH (e.g., LDHa, LDHb, or LDHc)polypeptides and nucleic acids include, but are not limited to, DQ912661(LDHa in CHO cells), BC067223 (human LDHa), BC084698 (rat LDHa),BC094428 (mouse LDHa), BC002362 (human LDHb), NM_012595 (rat LDHb),NM_008492 (mouse LDHb), BC090043 (human LDHc), NM_017266 (rat LDHc), andNM_013580 (mouse LDHc). Standard methods known by persons skill in theart can be used to determine whether a LDH polypeptide has LDH activityby measuring the ability of the polypeptide to convert pyruvate intolactate in vitro, in a cell extract, or in vivo.

Pryuvate dehydrogense kinase (PDHK) inhibits the conversion of pyruvateinto acetyl-CoA. The accession numbers of exemplary PDHK1 polypeptidesand nucleic acids include, but are not limited to, L42450 (human),BC089783 (rat), and NM_172665 (mouse). The accession numbers ofexemplary PDHK2 polypeptides and nucleic acids include, but are notlimited to, NM_002611 (human), NM_030872 (rat), and NM_133667 (mouse).The accession numbers of exemplary PDHK3 polypeptides and nucleic acidsinclude, but are not limited to, LA2452 (human), BC169078 (rat), andNM_145630 (mouse). The accession numbers of exemplary PDHK4 polypeptidesand nucleic acids include, but are not limited to, NM_002612 (human),NM_053551 (rat), and NM_013743 (mouse). Standard methods known by personskilled in the art can be used to determine whether a PDHK polypeptidehas PDHK activity by measuring the ability of the polypeptide to inhibitthe conversion of pyruvate into acetyl-CoA in vitro, in a cell extract,or in vivo.

Promoters are well known in the art. Any promoter that functions in thehost cell can be used for expression of siRNAs specific for a LDH andone or more of PDHK in the host cell. Virtually any promoter capable ofdriving these siRNAs is suitable for the present invention including,but not limited to, U6, H1, CYC1, HIS3, GAL1, GAL4, GAL10, ADH1, PGK,PHO5, GAPDH, T7, CMV, SV40, and EF1a. For example, in some embodiments,the method comprises a first heterologous nucleic acid sequence encodingan siRNA specific for LDHa, a second heterologous nucleic acid sequenceencoding an siRNA specific for PDHK1, a third heterologous nucleic acidsequence encoding an siRNA specific for PDHK2, and a fourth heterologousnucleic acid sequence encoding an siRNA specific for PDHK3, wherein thefirst heterologous nucleic acid sequence is operably linked to a firstpromoter U6, and wherein the second, third, and fourth heterologousnucleic acid sequences are operably linked to a second promoter H1. Inone variation, the first heterologous nucleic acid sequence encoding ansiRNA is specific for LDHb. In another variation, the first heterologousnucleic acid sequence encoding an siRNA is specific for LDHc.

In another aspect, provided is a method of making a cell that exhibitsdecreased lactate production in culture, comprising introducing into thecell a vector comprising a first heterologous nucleic acid sequenceencoding an siRNA specific for the LDH and a second heterologous nucleicacid sequence encoding an siRNA specific for the PDHK, wherein the firstheterologous nucleic acid sequence is operably linked to a firstpromoter, and wherein the second heterologous nucleic acid sequence isoperably linked to a second promoter.

The first heterologous nucleic acid sequence encoding an siRNA specificfor the LDH and the second heterologous nucleic acid sequence encodingthe siRNA specific for the PDHK can be inserted into a vector by avariety of procedures. For example, the LDH and PDHK siRNA sequences areligated to the desired position in the vector following digestion of theinsert and the vector with appropriate restriction endonucleases, suchas KasI, BamHI, HindIII, or BhIII. In some embodiments, a vectorcontaining siRNAs sequences specific for LDHa and PDHK1, PDHK2, andPDHK3 are constructed by inserting the LDHa siRNA sequence into the KasIsite of the vector (e.g., pSilencer 3.1-H1 hygro vector) with anaddition of U6 promoter at its immediate 5′end, inserting the PDHK1 andPDHK2 siRNA sequences into BamHI/HindIII and HindIII sites,respectively, and inserting the PDHK3 siRNA sequence into BgIII with anaddition of H1 promoter at the immediate 5′ends of PDHK1, PDHK2, andPDHK3. Cultured cells expressing decreased lactate production can thenbe generated by transfecting the vectors containing LDHa and PDHK1,PDHK2, and PDHK3 siRNA.

Compositions

The cultured cells produced by the methods described herein are alsoprovided in the present invention. The compositions of the presentinvention can be practiced in vivo, ex vivo, or in vitro. In one aspect,provided are cells in culture expressing a) an siRNA specific for LDHand b) an siRNA specific for a PDHK. In some embodiments, the culturedcells further express an siRNA specific for a second PDHK. In someembodiments, the cultured cells further express an siRNA specific for athird PDHK. In some embodiments, the cultured cells further express ansiRNA specific for a fourth PDHK.

In some embodiments, cells in culture express a) an siRNA specific forLDHa and b) an siRNA specific for PDHK1, PDHK2, and PDHK3, respectively.In some embodiments, cells in culture express a) an siRNA specific forLDHb and b) an siRNA specific for PDHK1, PDHK2, and PDHK3, respectively.In some embodiments, cells in culture express a) an siRNA specific forLDHc and b) an siRNA specific for PDHK1, PDHK2, and PDHK3, respectively.

In some embodiments, cells in culture express a) an siRNA specific forLDHa and b) an siRNA specific for two PDHKs, wherein the PDHK isselected from the group consisting of PDHK1, PDHK2, PDHK3, and PDHK4. Insome embodiments, cells in culture express a) an siRNA specific for LDHband b) an siRNA specific for two PDHKs, wherein the PDHK is selectedfrom the group consisting of PDHK1, PDHK2. PDHK3, and PDHK4. In someembodiments, cells in culture express a) an siRNA specific for LDHc andb) an siRNA specific for two PDHKs, wherein the PDHK is selected fromthe group consisting of PDHK1, PDHK2, PDHK3, and PDHK4.

In another aspect, provided are cells in culture comprising a firstheterologous nucleic acid sequence encoding an siRNA specific for a LDHand a second heterologous nucleic acid sequence encoding an siRNAspecific for a PDHK, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the secondheterologous nucleic acid sequence is operably linked to a secondpromoter. In some embodiments, the cells further comprise a thirdheterologous nucleic acid sequence encoding an siRNA specific for asecond PDHK and wherein the third heterologous nucleic acid sequence isoperably linked to a third promoter. In some embodiments, the cellsfurther comprise a fourth heterologous nucleic acid sequence encoding ansiRNA specific for a third PDHK and wherein the fourth heterologousnucleic acid sequence is operably linked to a fourth promoter. In someembodiments, the cells further comprise a fifth heterologous nucleicacid sequence encoding an siRNA specific for a fifth PDHK and whereinthe fifth heterologous nucleic acid sequence is operably linked to afifth promoter.

In some embodiments, cells in culture comprises a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter (e.g., U6), and whereinthe second, third, and fourth heterologous nucleic acid sequences areoperably linked to a second promoter (e.g., H1). In one variation, thefirst heterologous nucleic acid sequence encoding an siRNA is specificfor LDHb. In another variation, the first heterologous nucleic acidsequence encoding an siRNA is specific for LDHb.

In some embodiments, cells in culture comprise a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for aPDHK, a third heterologous nucleic acid sequence encoding an siRNAspecific for a PDHK, wherein the PDHK is selected from the groupconsisting of PDHK1, PDHK2, PDHK3, and PDHK4, wherein the firstheterologous nucleic acid sequence is operably linked to a firstpromoter (e.g., U6), and wherein the second and the third heterologousnucleic acid sequences are operably linked to a second promoter (e.g.,H1). In one variation, the first heterologous nucleic acid sequenceencoding an siRNA is specific for LDHb. In another variation, the firstheterologous nucleic acid sequence encoding an siRNA is specific forLDHc.

In some embodiments, the cell culture includes at least about 5, 10, 15,20, 50, 75, 100, 200, 500, 750, 1,000, 5,000, 7,500, 10,000, 15,000 ormore cells.

In another aspect, provided are cells in culture having a lactatesynthesis rate that is lower than a lactate consumption rate. In someembodiments, the cells in culture have an average lactate productionrate of less than about any of negative 0.2 mg/10⁶ cells/day, negative0.1 mg/10⁶ cells/day, negative 0.08 mg/10⁶ cells/day, negative 0.06mg/10⁶ cells/day, negative 0.04 mg/10⁶ cells/day, negative 0.02 mg/10⁶cells/day, negative 0.01 mg/10⁶ cells/day, negative 0.008 mg/10cells/day, negative 0.006 mg/10⁶ cells/day, negative 0.004 mg/10⁶cells/day, or negative 0.002 mg/10⁶ cells/day.

In some embodiments, cells in culture comprises a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter (e.g., U6), wherein thesecond, third, and fourth heterologous nucleic acid sequences areoperably linked to a second promoter (e.g., H1), and wherein the cellsin culture have an average lactate production rate of about negative0.02 mg/10⁶ cells/day.

In another aspect, provided are cells in culture containing siRNAspecific for a LDH and PDHK(s) having a decreased osmolality. In someembodiments, cells in culture containing siRNA specific for a LDH andPDHK(s) have an osmolality at less than about any of 500 mOsm, 450 mOsm,400 mOsm 350 mOsm, 300 mOsm, 250 mOsm, 200 mOsm, or 150 mOsm.

In some embodiments, cells in culture comprises a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter (e.g., U6), wherein thesecond, third, and fourth heterologous nucleic acid sequence is operablylinked to a second promoter (e.g., H1), and wherein the cells in culturehave an osmolality at about 300 mOsm.

In another aspect, provided are cells in culture having an increasedSpecific Productivity (Qp). In some embodiments, the cultured cells havea Specific Productivity of at least about 60% higher, at least about 65%higher, at least about 70% higher, at least about 75% higher, at leastabout 80% higher, at least about 85% higher, at least about 90% higher,or at least about 95% higher than cultured cells without theheterologous nucleic acid sequence comprising the PDHK(s) and the LDH.In some embodiments, the cultured cells have a Specific Productivity ofabout 67% higher, about 69% higher, about 71% higher, about 72% higher,about 73% higher, about 74% higher, about 75% higher, about 76% higher,about 77% higher, about 78% higher, about 79% higher, about 81% higher,about 83% higher, about 85% higher, about 87% higher, about 89% higher,about 91% higher, about 93% higher, about 95% higher, about 97% higher,or at about 99% higher than cultured cells without the heterologousnucleic acid sequence comprising the PDHK(s) and the LDH.

In some embodiments, cells in culture comprises a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter (e.g., U6), wherein thesecond, third, and fourth heterologous nucleic acid sequence is operablylinked to a second promoter (e.g., H1), and wherein the cells in culturehave a Specific Productivity of about 75% higher.

In another aspect, provided are the cultured cells produced by themethod herein with an increased polypeptide productivity (e.g., antibodyproductivity or titer in g/L). In some embodiments, the cultured cellshave a polypeptide productivity of about 10% to about 800% higher thancultured cells without the heterologous nucleic acid sequence comprisingthe PDHK(s) and the LDH. In some embodiments, the cultured cells have apolypeptide productivity of about 10% higher, about 15% higher, about20% higher, about 25% higher, about 30% higher, about 35% higher, about40% higher, about 45% higher, about 50% higher, about 55% higher, about58% higher, about 60% higher, about 65% higher, about 70% higher, about71% higher, about 75% higher, about 80% higher, about 85% higher, about90% higher, about 95% higher, about 100% higher, about 125% higher,about 150%, about 200% higher, about 250% higher, about 300% higher,about 350% higher, about 400% higher, about 450% higher, about 500higher, about 550% higher, about 600% higher, about 650% higher, about700% higher, about 750% higher, or about 800% higher than cultured cellswithout the heterologous nucleic acid sequence comprising the PDHK(s)and the LDH. In some embodiments, the cultured cells have a polypeptideproductivity of at least about 55% higher, at least about 60% higher, atleast about 65% higher, at least about 68% higher, at least about 70%higher, at least about 80% higher, at least about 85% higher, or atleast about 90% higher than cultured cells without the heterologousnucleic acid sequence comprising the PDHK(s) and the LDH.

In some embodiments, cells in culture comprises a first heterologousnucleic acid sequence encoding an siRNA specific for LDHa, a secondheterologous nucleic acid sequence encoding an siRNA specific for PDHK1,a third heterologous nucleic acid sequence encoding an siRNA specificfor PDHK2, and a fourth heterologous nucleic acid sequence encoding ansiRNA specific for PDHK3, wherein the first heterologous nucleic acidsequence is operably linked to a first promoter (e.g., U6), wherein thesecond, third, and fourth heterologous nucleic acid sequence is operablylinked to a second promoter (e.g., H1), and wherein the cultured cellshave an antibody productivity (e.g., in g/L) of at least about 68%higher than cultured cells without the heterologous nucleic acidsequence comprising the PDHK1, PDHK2, PDHK3, and LDHa.

In some embodiments, the cultured cells have a polypeptide productivityof about 10% to about 800% higher than cultured cells without the siRNAsspecific for the PDHK(s) and the LDH (in some embodiments, an antibody).In some embodiments, the cultured cells have a polypeptide productivityof about 10% higher, about 15% higher, about 20% higher, about 25%higher, about 30% higher, about 35% higher, about 40% higher, about 45%higher, about 50% higher, about 55% higher, about 60% higher, about 65%higher, about 70% higher, about 75% higher, about 80% higher, about 85%higher, about 90% higher, about 95% higher, about 100% higher, about125% higher, about 150%, about 200% higher, about 250% higher, about300% higher, about 350% higher, about 400% higher, about 450% higher,about 500 higher, about 550% higher, about 600% higher, about 650%higher, about 700% higher, about 750% higher, or about 800% higher thancultured cells without the siRNAs specific for the PDHK(s) and the LDH.In some embodiments, the cultured cells have a polypeptide productivityof at least about 65% higher, at least about 68% higher, at least about70% higher, at least about 80% higher, at least about 85% higher, or atleast about 90% higher than cultured cells w without the siRNAs specificfor the PDHK(s) and the LDH. In some embodiments, the antibodyproductivity is at least about 68% higher than cultured cells withoutthe siRNAs specific for the PDHK(s) and the LDH.

In another aspect, provided is a vector comprising a first heterologousnucleic acid sequence encoding an siRNA specific for a LDH and a secondheterologous nucleic acid sequence encoding an siRNA specific for aPDHK, wherein the first heterologous nucleic acid sequence is operablylinked to a first promoter, and wherein the second heterologous nucleicacid sequence is operably linked to a second promoter.

In some embodiments, the vector contains a nucleic acid under thecontrol of an expression control sequence. As used herein, an“expression control sequence” means a nucleic acid sequence that directstranscription of a nucleic acid of interest. An expression controlsequence can be a promoter, such as a constitutive or an induciblepromoter, or an enhancer. An “inducible promoter” is a promoter that isactive under environmental or developmental regulation. The expressioncontrol sequence is operably linked to the nucleic acid segment to betranscribed.

In some embodiments, the vector also includes a termination sequence.Termination control regions may also be derived from various genesnative to the host cell. In some embodiments, the termination sequenceand the promoter sequence are derived from the same source. In anotherembodiment, the termination sequence is endogenous to the host cell.Optionally, a termination site may be included. For effective expressionof the polypeptides, DNA encoding the polypeptide are linked operablythrough initiation codons to selected expression control regions suchthat expression results in the formation of the appropriate messengerRNA.

In some embodiments, the vector contains a selective marker. The term“selective marker” refers to a nucleic acid capable of expression in ahost cell that allows for ease of selection of those host cellscontaining an introduced nucleic acid or vector. Examples of selectablemarkers include, but are not limited to, antibiotic resistance nucleicacids (e.g., kanamycin, ampicillin, carbenicillin, gentamicin,hygromycin, phleomycin, bleomycin, neomycin, or chloramphenicol) and/ornucleic acids that confer a metabolic advantage, such as a nutritionaladvantage on the host cell. In some embodiments, the selective marker isthe hygromycin nucleic acid.

Polypeptides

The polypeptide or protein to be produced using the methods and culturedcells described herein includes, but is not limited to, antibody orimmunoadhesin. Techniques for generating such molecules are discussedbelow.

Antibodies

Antibodies within the scope of the present invention include, but arenot limited to: anti-CD20 antibodies such as chimeric anti-CD20 “C2B8”as in U.S. Pat. No. 5,736,137 (RITUXAN®); anti-VEGF antibodies,including humanized and/or affinity matured anti-VEGF antibodies such asthe humanized anti-VEGF antibody huA4.6.1 AVASTIN (Kim et al., GrowthFactors, 7:53-64 (1992), International Publication No. WO 96/30046, andWO 98/45331, published Oct. 15, 1998) and V3LA; anti-MUC16 antibody;anti-CD4 antibodies such as the cM-7412 antibody (Choy et al. ArthritisRheum. 39(1):52-56 (1996)) and the Ibalizumab (TNX355) antibody;anti-MET antibodies such as one-armed 5D5 anti-C-Met antibody; anti-HER2antibodies Trastuzumab (HERCEPTIN®) (Carter et al., Proc. Natl. Acad.Sci. USA, 89:4285-4289 (1992), U.S. Pat. No. 5,725,856) and humanized2C4 (WO01/00245, Adams et al.), a chimeric or humanized variant of the2H7 antibody as in U.S. Pat. No. 5,721,108B1, or Tositumomab (BEXXAR®);anti-IL-8 antibodies (St John et al., Chest, 103:932 (1993), andInternational Publication No. WO 95/23865); anti-prostate stem cellantigen (PSCA) antibodies (WO01/40309); anti-CD40 antibodies, includingS2C6 and humanized variants thereof (WO00/75348); anti-CD1 antibodies(U.S. Pat. No. 5,622,700, WO 98/23761, Steppe et al., Transplant Intl.4:3-7 (1991), and Hourmant et al., Transplantation 58:377-380 (1994));anti-CD18 (U.S. Pat. No. 5,622,700, issued Apr. 22, 1997, or as in WO97/26912, published Jul. 31, 1997); anti-IgE antibodies (including E25,E26 and E27; U.S. Pat. No. 5,714,338, issued Feb. 3, 1998 or U.S. Pat.No. 5,091,313, issued Feb. 25, 1992, WO 93/04173 published Mar. 4, 1993,or International Application No. PCT/US98/13410 filed Jun. 30, 1998,U.S. Pat. No. 5,714,338, Presta et al., J. Immunol. 151:2623-2632(1993), and International Publication No. WO 95/19181); anti-Apo-2receptor antibodies (WO 98/51793 published Nov. 19, 1998); anti-TNF-αantibodies, including cA2 (REMICADE®), CDP571 and MAK-195 (See, U.S.Pat. No. 5,672,347 issued Sep. 30, 1997, Lorenz et al. J. Immunol.156(4):1646-1653(1996), and Dhainaut et al. Crit. Care Med.23(9):1461-1469 (1995)); anti-Tissue Factor (TF) antibodies (EuropeanPatent No. 0 420 937 B1 granted Nov. 9, 1994); anti-human α4β7 integrinantibodies (WO 98/06248 published Feb. 19, 1998); anti-epidermal growthfactor receptor (EGFR) antibodies (e.g. chimerized or humanized 225antibody as in WO 96/40210 published Dec. 19, 1996); anti-CD3 antibodiessuch as OKT3 (U.S. Pat. No. 4,515,893 issued May 7, 1985); anti-CD25 oranti-Tac antibodies such as CHI-621 (SIMULECT® and ZENAPAX® (See U.S.Pat. No. 5,693,762 issued Dec. 2, 1997); anti-CD52 antibodies such asCAMPATH-1H (Riechmann et al. Nature 332:323-337 (1988)); anti-Fcreceptor antibodies such as the M22 antibody directed against Fcy RI asin Graziano et al. J. Immunol. 155(10):4996-5002 (1995);anti-carcinoembryonic antigen (CEA) antibodies such as hMN-1 4 (Sharkeyet al. Cancer Res. 55(23 Suppl): 5935s-5945s (1995); antibodies directedagainst breast epithelial cells including huBrE-3, hu-Mc 3 and CHL6(Ceriani et al. Cancer Res. 55(23): 5852s-5856s (1995); and Richman etal. Cancer Res. 55(23 Supp): 5916s-5920s (1995)); antibodies that bindto colon carcinoma cells such as C242 (Litton et al. Eur J Immunol.26(1): 1-9 (1996)); anti-CD38 antibodies, e.g. AT 13/5 (Ellis et al. J.Immunol. 155(2):925-937 (1995)); anti-CD33 antibodies such as Hu M195(Jurcic et al. Cancer Res 55(23 Suppl):5908s-5910s (1995) and CMA-676 orCDP771; anti-CD22 antibodies such as LL2 or LymphoCide (Juweid et al.Cancer Res 55(23 Suppl):5899s-5907s (1995)); anti-EpCAM antibodies suchas 17-1A (PANOREX®); anti-GpIIb/IIIa antibodies such as abciximab orc7E3 Fab (REOPRO®); anti-RSV antibodies such as MEDI-493 (SYNAGIS®);anti-CMV antibodies such as PROTOVIR®; anti-HIV antibodies such asPRO542; anti-hepatitis antibodies such as the anti-Hep B antibodyOSTAVIR®; anti-CA 125 antibodies, such as OvaRex; anti-idiotypic GD3epitope antibody BEC2; anti-αvβ3 antibodies, including VITAXIN®;anti-human renal cell carcinoma antibody such as ch-G250; ING-1;anti-human 17-1A antibody (3622W94): anti-human colorectal tumorantibody (A33); anti-human melanoma antibody R24 directed against GD3ganglioside; anti-human squamous-cell carcinoma (SF-25); and anti-humanleukocyte antigen (HLA) antibodies such as Smart ID10 and the anti-HLADR antibody Oncolym (Lym-1).

Aside from the antibodies specifically identified above, the skilledpractitioner can generate antibodies directed against an antigen ofinterest, e.g., using the techniques described below.

(i) Antigen Selection and Preparation

The antibody herein is directed against an antigen of interest.Preferably, the antigen is a biologically important polypeptide andadministration of the antibody to a mammal suffering from a disease ordisorder can result in a therapeutic benefit in that mammal. However,antibodies directed against nonpolypeptide antigens (such astumor-associated glycolipid antigens; see U.S. Pat. No. 5,091,178) arealso contemplated. Where the antigen is a polypeptide, it may be atransmembrane molecule (e.g. receptor) or ligand such as a growthfactor. Exemplary antigens include those proteins described in section(3) below. Exemplary molecular targets for antibodies encompassed by thepresent invention include CD proteins such as CD3, CD4, CD8, CD19, CD20,CD22 and CD34; members of the ErbB receptor family such as the EGFR,HER2, HER3 or HER4 receptor; cell adhesion molecules such as LFA-1,Mac1, p1 50,95, VLA-4, ICAM-1, VCAM and αv/β3 integrin including eitherα or β subunits thereof (e.g. anti-CD11a, anti-CD18 or anti-CD11bantibodies); growth factors such as VEGF; IgE; blood group antigens;flk2/flt3 receptor, obesity (OB) receptor; mp1 receptor; CTLA-4; proteinC, or any of the other antigens mentioned herein.

Soluble antigens or fragments thereof, optionally conjugated to othermolecules, can be used as immunogens for generating antibodies. Fortransmembrane molecules, such as receptors, fragments of these (e.g. theextracellular domain of a receptor) can be used as the immunogen.Alternatively, cells expressing the transmembrane molecule can be usedas the immunogen. Such cells can be derived from a natural source (e.g.cancer cell lines) or may be cells which have been transformed byrecombinant techniques to express the transmembrane molecule.

Other antigens and forms thereof useful for preparing antibodies will beapparent to those in the art.

(ii) Polyclonal Antibodies

Polyclonal antibodies are preferably raised in animals by multiplesubcutaneous (sc) or intraperitoneal (ip) injections of the relevantantigen and an adjuvant. It may be useful to conjugate the antigen to aprotein that is immunogenic in the species to be immunized, e.g.,keyhole limpet hemocyanin, serum albumin, bovine thyroglobulin, orsoybean trypsin inhibitor using a bifunctional or derivatizing agent,for example, maleimidobenzoyl sulfosuccinimide ester (conjugationthrough cysteine residues). N-hydroxysuccinimide (through lysineresidues), glutaraldehyde, succinic anhydride, SOCl₂, or R¹N═C═NR, whereR and R¹ are different alkyl groups.

Animals are immunized against the antigen, immunogenic conjugates, orderivatives by combining, e.g., 100 μg or 5 μg of the protein orconjugate (for rabbits or mice, respectively) with 3 volumes of Freund'scomplete adjuvant and injecting the solution intradermally at multiplesites. One month later the animals are boosted with ⅕ to (fraction (1/10)) the original amount of antigen or conjugate in Freund's completeadjuvant by subcutaneous injection at multiple sites. Seven to 14 dayslater the animals are bled and the serum is assayed for antibody titer.Animals are boosted until the titer plateaus. Preferably, the animal isboosted with the conjugate of the same antigen, but conjugated to adifferent protein and/or through a different cross-linking reagent.Conjugates also can be made in recombinant cell culture as proteinfusions. Also, aggregating agents such as alum are suitably used toenhance the immune response.

(iii) Monoclonal Antibodies

Monoclonal antibodies may be made using the hybridoma method firstdescribed by Kohler et al., Nature, 256:495 (1975), or may be made byrecombinant DNA methods (U.S. Pat. No. 4,816,567).

In the hybridoma method, a mouse or other appropriate host animal, suchas a hamster or macaque monkey, is immunized as hereinabove described toelicit lymphocytes that produce or are capable of producing antibodiesthat will specifically bind to the protein used for immunization.Alternatively, lymphocytes may be immunized in vitro.

Lymphocytes then are fused with myeloma cells using a suitable fusingagent, such as polyethylene glycol, to form a hybridoma cell (Goding,Monoclonal Antibodies: Principles and Practice, pp. 59-103 (AcademicPress, 1986)).

The hybridoma cells thus prepared are seeded and grown in a suitableculture medium that preferably contains one or more substances thatinhibit the growth or survival of the unfused, parental myeloma cells.For example, if the parental myeloma cells lack the enzyme hypoxanthineguanine phosphoribosyl transferase (HGPRT or HPRT), the culture mediumfor the hybridomas typically will include hypoxanthine, aminopterin, andthymidine (HAT medium), which substances prevent the growth ofHGPRT-deficient cells.

Preferred myeloma cells are those that fuse efficiently, support stablehigh-level production of antibody by the selected antibody-producingcells, and are sensitive to a medium such as HAT medium. Among these,preferred myeloma cell lines are murine myeloma lines, such as thosederived from MOPC-21 and MPC-11 mouse tumors available from the SalkInstitute Cell Distribution Center, San Diego. Calif. USA, and SP-2 orX63-Ag8-653 cells available from the American Type Culture Collection,Rockville, Md. USA. Human myeloma and mouse-human heteromyeloma celllines also have been described for the production of human monoclonalantibodies (Kozbor, J. Immunol., 133:3(001 (1984); Brodeur et al,Monoclonal Antibody Production Techniques and Applications, pp. 51-63(Marcel Dekker, Inc., New York, 1987)).

Culture medium in which hybridoma cells are growing is assayed forproduction of monoclonal antibodies directed against the antigen.Preferably, the binding specificity of monoclonal antibodies produced byhybridoma cells is determined by immunoprecipitation or by an in vitrobinding assay, such as radioimmunoassay (RIA) or enzyme-linkedimmunoabsorbent assay (ELISA).

After hybridoma cells are identified that produce antibodies of thedesired specificity, affinity, and/or activity, the clones may besubcloned by limiting dilution procedures and grown by standard methods(Goding, Monoclonal Antibodies: Principles and Practice, pp. 59-103(Academic Press, 1986)). Suitable culture media for this purposeinclude, for example, D-MEM or RPMI-1640 medium. In addition, thehybridoma cells may be grown in vivo as ascites tumors in an animal.

The monoclonal antibodies secreted by the subclones are suitablyseparated from the culture medium, ascites fluid, or serum byconventional immunoglobulin purification procedures such as, forexample, Protein A-Sepharose, hydroxylapatite chromatography, gelelectrophoresis, dialysis, or affinity chromatography. Preferably theProtein A affinity chromatography procedure using a pH gradientdescribed herein is used.

DNA encoding the monoclonal antibodies is readily isolated and sequencedusing conventional procedures (e.g., by using oligonucleotide probesthat are capable of binding specifically to genes encoding the heavy andlight chains of the monoclonal antibodies). The hybridoma cells serve asa preferred source of such DNA. Once isolated, the DNA may be placedinto expression vectors, which are then transfected into host cells suchas E. coli cells, simian COS cells, Chinese hamster ovary (CHO) cells,or myeloma cells that do not otherwise produce immunoglobulin protein,to obtain the synthesis of monoclonal antibodies in the recombinant hostcells.

The DNA also may be modified, for example, by substituting the codingsequence for human heavy- and light-chain constant domains in place ofthe homologous murine sequences (U.S. Pat. No. 4,816,567; Morrison, etal., Proc. Natl Acad. Sci. USA, 81:6851 (1984)), or by covalentlyjoining to the immunoglobulin coding sequence all or part of the codingsequence for a non-immunoglobulin polypeptide.

Typically such non-immunoglobulin polypeptides are substituted for theconstant domains of an antibody, or they are substituted for thevariable domains of one antigen-combining site of an antibody to createa chimeric bivalent antibody comprising one antigen-combining sitehaving specificity for an antigen and another antigen-combining sitehaving specificity for a different antigen.

Monoclonal antibodies can be isolated from antibody phage librariesgenerated using the techniques described in McCafferty et al., Nature,348:552-554 (1990). Clackson et al., Nature, 352:624-628 (1991) andMarks et al., J. Mol. Biol., 222:581-597 (1991) describe the isolationof murine and human antibodies, respectively, using phage libraries.Subsequent publications describe the production of high affinity (nMrange) human antibodies by chain shuffling (Marks et al.,Bio/Technology, 10:779-783 (1992)), as well as combinatorial infectionand in vivo recombination as a strategy for constructing very largephage libraries (Waterhouse et al., Nuc. Acids. Res., 21:2265-2266(1993)). Thus, these techniques are viable alternatives to traditionalhybridoma techniques for isolation of monoclonal antibodies.

(iv) Humanized and Human Antibodies

A humanized antibody has one or more amino acid residues introduced intoit from a source which is non-human. These non-human amino acid residuesare often referred to as “import” residues, which are typically takenfrom an “import” variable domain. Humanization can be essentiallyperformed following the method of Winter and co-workers (Jones et al.,Nature, 321:522-525 (1986); Riechmann et al., Nature, 332:323-327(1988); Verhoeyen et al., Science, 239:1534-1536 (1988)), bysubstituting rodent CDRs or CDR sequences for the correspondingsequences of a human antibody. Accordingly, such “humanized” antibodiesare chimeric antibodies (U.S. Pat. No. 4,816,567) wherein substantiallyless than an intact human variable domain has been substituted by thecorresponding sequence from a non-human species. In practice, humanizedantibodies are typically human antibodies in which some CDR residues andpossibly some FR residues are substituted by residues from analogoussites in rodent antibodies.

The choice of human variable domains, both light and heavy, to be usedin making the humanized antibodies is very important to reduceantigenicity. According to the so-called “best-fit” method, the sequenceof the variable domain of a rodent antibody is screened against theentire library of known human variable-domain sequences. The humansequence which is closest to that of the rodent is then accepted as thehuman FR for the humanized antibody (Sims et al., J. Immunol., 151:2296(1993)). Another method uses a particular framework derived from theconsensus sequence of all human antibodies of a particular subgroup oflight or heavy chains. The same framework may be used for severaldifferent humanized antibodies (Carter et al., Proc. Natl. Acad. Sci.USA. 89:4285 (1992); Presta et al., J. Immnol., 151:2623 (1993)).

It is further important that antibodies be humanized with retention ofhigh affinity for the antigen and other favorable biological properties.To achieve this goal, according to a preferred method, humanizedantibodies are prepared by a process of analysis of the parentalsequences and various conceptual humanized products usingthree-dimensional models of the parental and humanized sequences.Three-dimensional immunoglobulin models are commonly available and arefamiliar to those skilled in the art. Computer programs are availablewhich illustrate and display probable three-dimensional conformationalstructures of selected candidate immunoglobulin sequences. Inspection ofthese displays permits analysis of the likely role of the residues inthe functioning of the candidate immunoglobulin sequence, i.e., theanalysis of residues that influence the ability of the candidateimmunoglobulin to bind its antigen. In this way, FR residues can beselected and combined from the recipient and import sequences so thatthe desired antibody characteristic, such as increased affinity for thetarget antigen(s), is achieved. In general, the CDR residues aredirectly and most substantially involved in influencing antigen binding.

Alternatively, it is now possible to produce transgenic animals (e.g.,mice) that are capable, upon immunization, of producing a fullrepertoire of human antibodies in the absence of endogenousimmunoglobulin production. For example, it has been described that thehomozygous deletion of the antibody heavy-chain joining region (JH) genein chimeric and germ-line mutant mice results in complete inhibition ofendogenous antibody production. Transfer of the human germ-lineimmunoglobulin gene array in such germ-line mutant mice will result inthe production of human antibodies upon antigen challenge. See, e.g.,Jakobovits et al., Proc. Natl. Acad. Sci. USA, 90:2551 (1993);Jakobovits et al., Nature. 362:255-258 (1993); Bruggermann et al., Yearin Immuno., 7:33 (1993); and Duchosal et al. Nature 355:258 (1992).Human antibodies can also be derived from phage-display libraries(Hoogenboom et al., J. Mol. Biol., 227:381 (1991); Marks et al., J. Mol.Biol., 222:581-597 (1991): Vaughan et al. Nature Biotech 14:309 (1996)).

(v) Antibody Fragments

Various techniques have been developed for the production of antibodyfragments. Traditionally, these fragments were derived via proteolyticdigestion of intact antibodies (see, e.g., Morimoto et al. Journal ofBiochemical and Biophysical Methods 24:107-117 (1992) and Brennan etal., Science. 229:81 (1985)). However, these fragments can now beproduced directly by recombinant host cells. For example, the antibodyfragments can be isolated from the antibody phage libraries discussedabove. Alternatively, Fab′-SH fragments can be directly recovered fromE. coli and chemically coupled to form F(ab′)₂ fragments (Carter et al.,Bio/Technology 10:163-167 (1992)). According to another approach,F(ab′)₂ fragments can be isolated directly from recombinant host cellculture. A single chain Fv fragment (scFv) can also be isolated. See WO93/16185. Other techniques for the production of antibody fragments willbe apparent to the skilled practitioner.

(vi) Multispecific Antibodies

Multispecific antibodies have binding specificities for at least twodifferent antigens. While such molecules normally will only bind twoantigens (i.e. bispecific antibodies, BsAbs), antibodies with additionalspecificities such as trispecific antibodies are encompassed by thisexpression when used herein.

Methods for making bispecific antibodies are known in the art.Traditional production of full length bispecific antibodies is based onthe coexpression of two immunoglobulin heavy chain-light chain pairs,where the two chains have different specificities (Millstein et al.,Nature, 305:537-539 (1983)). Because of the random assortment ofimmunoglobulin heavy and light chains, these hybridomas (quadromas)produce a potential mixture of 10 different antibody molecules, of whichonly one has the correct bispecific structure. Purification of thecorrect molecule, which is usually done by affinity chromatographysteps, is rather cumbersome, and the product yields are low. Similarprocedures are disclosed in WO 93/08829, and in Traunecker et al., EMBOJ., 10:3655-3659 (1991).

According to another approach described in WO96/27011, the interfacebetween a pair of antibody molecules can be engineered to maximize thepercentage of heterodimers which are recovered from recombinant cellculture. The preferred interface comprises at least a part of the C_(H)3domain of an antibody constant domain. In this method, one or more smallamino acid side chains from the interface of the first antibody moleculeare replaced with larger side chains (e.g., tyrosine or tryptophan).Compensatory “cavities” of identical or similar size to the large sidechain(s) are created on the interface of the second antibody molecule byreplacing large amino acid side chains with smaller ones (e.g., alanineor threonine). This provides a mechanism for increasing the yield of theheterodimer over other unwanted end-products such as homodimers.

Bispecific antibodies include cross-linked or “heteroconjugate”antibodies. For example, one of the antibodies in the heteroconjugatecan be coupled to avidin, the other to biotin. Such antibodies have, forexample, been proposed to target immune system cells to unwanted cells(U.S. Pat. No. 4,676,980), and for treatment of HIV infection (WO91/00360, WO 92/200373, and EP 03089). Heteroconjugate antibodies may bemade using any convenient cross-linking methods. Suitable cross-linkingagents are well known in the art, and are disclosed in U.S. Pat. No.4,676,980, along with a number of cross-linking techniques.

Techniques for generating bispecific antibodies from antibody fragmentshave also been described in the literature. For example, bispecificantibodies can be prepared using chemical linkage. Brennan et al.,Science. 229: 81 (1985) describe a procedure wherein intact antibodiesare proteolytically cleaved to generate F(ab′)2 fragments. Thesefragments are reduced in the presence of the dithiol complexing agentsodium arsenite to stabilize vicinal dithiols and prevent intermoleculardisulfide formation. The Fab′ fragments generated are then converted tothionitrobenzoate (TNB) derivatives. One of the Fab′-TNB derivatives isthen reconverted to the Fab′-thiol by reduction with mercaptoethylamineand is mixed with an equimolar amount of the other Fab′-TNB derivativeto form the bispecific antibody. The bispecific antibodies produced canbe used as agents for the selective immobilization of enzymes.

Recent progress has facilitated the direct recovery of Fab′-SH fragmentsfrom E. coli, which can be chemically coupled to form bispecificantibodies. Shalaby et al., J. Exp. Med., 175: 217-225 (1992) describethe production of a fully humanized bispecific antibody F(ab′)₂molecule. Each Fab′ fragment was separately secreted from E. coli andsubjected to directed chemical coupling in vitro to form the bispecificantibody. The bispecific antibody thus formed was able to bind to cellsoverexpressing the ErbB2 receptor and normal human T cells, as well astrigger the lytic activity of human cytotoxic lymphocytes against humanbreast tumor targets.

Various techniques for making and isolating bispecific antibodyfragments directly from recombinant cell culture have also beendescribed. For example, bispecific antibodies have been produced usingleucine zippers. Kostelny et al., J. Immunol., 148(5):1547-1553 (1992).The leucine zipper peptides from the Fos and Jun proteins were linked tothe Fab′ portions of two different antibodies by gene fusion. Theantibody homodimers were reduced at the hinge region to form monomersand then re-oxidized to form the antibody heterodimers. This method canalso be utilized for the production of antibody homodimers. The“diabody” technology described by Hollinger et al., Proc. Natl. Acad.Sci. USA, 90:6444-6448 (1993) has provided an alternative mechanism formaking bispecific antibody fragments. The fragments comprise aheavy-chain variable domain (Vii) connected to a light-chain variabledomain (V_(L)) by a linker which is too short to allow pairing betweenthe two domains on the same chain. Accordingly, the V_(H) and V₁,domains of one fragment are forced to pair with the complementary V_(L)and V_(H) domains of another fragment, thereby forming twoantigen-binding sites. Another strategy for making bispecific antibodyfragments by the use of single-chain Fv (sFv) dimers has also beenreported. See Gruber et al., J. Immunol., 152:5368 (1994).Alternatively, the antibodies can be “linear antibodies” as described inZapata et al. Protein Eng. 8(10): 1057-1062 (1995). Briefly, theseantibodies comprise a pair of tandem Fd segments (V_(H)-C_(H)1-V_(H) andV_(L)) which form a pair of antigen binding regions. Linear antibodiescan be bispecific or monospecific.

Antibodies with more than two valencies are contemplated. For example,trispecific antibodies can be prepared. Tutt et al. J. Immunol 147: 60(1991).

Immunoadhesins

The simplest and most straightforward immunoadhesin design combines thebinding domain(s) of the adhesin (e.g., the extracellular domain (ECD)of a receptor) with the hinge and Fc regions of an immunoglobulin heavychain. Ordinarily, when preparing the immunoadhesins of the presentinvention, nucleic acid encoding the binding domain of the adhesin willbe fused C-terminally to nucleic acid encoding the N-terminus of animmunoglobulin constant domain sequence, however N-terminal fusions arealso possible.

Typically, in such fusions the encoded chimeric polypeptide will retainat least functionally active hinge, C_(H)2 and C_(H)3 domains of theconstant region of an immunoglobulin heavy chain. Fusions are also madeto the C-terminus of the Fc portion of a constant domain, or immediatelyN-terminal to the C_(H)1 of the heavy chain or the corresponding regionof the light chain. The precise site at which the fusion is made is notcritical; particular sites are well known and may be selected in orderto optimize the biological activity, secretion, or bindingcharacteristics of the immunoadhesin.

In some embodiments, the adhesin sequence is fused to the N-terminus ofthe Fc domain of immunoglobulin G₁ (Ig G₁). It is possible to fuse theentire heavy chain constant region to the adhesin sequence. However,preferably, a sequence beginning in the hinge region just upstream ofthe papain cleavage site which defines IgG Fc chemically (i.e. residue216, taking the first residue of heavy chain constant region to be 114),or analogous sites of other immunoglobulins is used in the fusion. Insome embodiments, the adhesin amino acid sequence is fused to (a) thehinge region and or C_(H)2 and C_(H)3 or (b) the C_(H)1, hinge, C_(H)2and C_(H)3 domains, of an IgG heavy chain.

For bispecific immunoadhesins, the immunoadhesins are assembled asmultimers, and particularly as heterodimers or heterotetramers.Generally, these assembled immunoglobulins will have known unitstructures. A basic four chain structural unit is the form in which IgG,IgD, and IgE exist. A four chain unit is repeated in the highermolecular weight immunoglobulins; IgM generally exists as a pentamer offour basic units held together by disulfide bonds. IgA globulin, andoccasionally IgG globulin, may also exist in multimeric form in serum.In the case of multimer, each of the four units may be the same ordifferent.

Various exemplary assembled immunoadhesins within the scope herein areschematically diagramed below:

(a) AC_(L)-AC_(L);

(b) AC_(H)-(AC_(H), AC_(L)-AC_(H), AC_(L)-V_(H)C_(H), orV_(L)C_(L)-AC_(H));

(c) AC_(L)-AC_(H)-(AC_(L)-AC_(H), AC_(L)-V_(H)C_(H), V_(L)C_(L)-AC_(H),or V_(L)C_(L)-V_(H)C_(H))

(d) AC_(L)-V_(H)C_(H)-(AC_(H), or AC_(L)-V_(H)C_(H), orV_(L)C_(L)-AC_(H));

(e) V_(L)C_(L)-AC_(H)-(AC_(L)-V_(H) C_(H), or V_(L)C_(L)-AC_(H)); and

(f) (A-Y)_(n)-(V_(L)C_(L)-V_(H)C_(H))₂.

wherein each A represents identical or different adhesin amino acidsequences;

V_(L) is an immunoglobulin light chain variable domain;

V_(H) is an immunoglobulin heavy chain variable domain;

C_(L), is an immunoglobulin light chain constant domain;

C_(H) is an immunoglobulin heavy chain constant domain;

n is an integer greater than 1;

Y designates the residue of a covalent cross-linking agent.

In the interests of brevity, the foregoing structures only show keyfeatures; they do not indicate joining (J) or other domains of theimmunoglobulins, nor are disulfide bonds shown. However, where suchdomains are required for binding activity, they shall be constructed tobe present in the ordinary locations which they occupy in theimmunoglobulin molecules.

Alternatively, the adhesin sequences can be inserted betweenimmunoglobulin heavy chain and light chain sequences, such that animmunoglobulin comprising a chimeric heavy chain is obtained. In thisembodiment, the adhesin sequences are fused to the 3′ end of animmunoglobulin heavy chain in each arm of an immunoglobulin, eitherbetween the hinge and the C_(H)2 domain, or between the C_(H)2 andC_(H)3 domains. Similar constructs have been reported by Hoogenboom, etal., Mol. Immunol. 28:1027-1037 (1991).

Although the presence of an immunoglobulin light chain is not requiredin the immunoadhesins of the present invention, an immunoglobulin lightchain might be present either covalently associated to anadhesin-immunoglobulin heavy chain fusion polypeptide, or directly fusedto the adhesin. In the former case. DNA encoding an immunoglobulin lightchain is typically coexpressed with the DNA encoding theadhesin-immunoglobulin heavy chain fusion protein. Upon secretion, thehybrid heavy chain and the light chain will be covalently associated toprovide an immunoglobulin-like structure comprising two disulfide-linkedimmunoglobulin heavy chain-light chain pairs. Methods suitable for thepreparation of such structures are, for example, disclosed in U.S. Pat.No. 4,816,567, issued 28 Mar. 1989.

Immunoadhesins are most conveniently constructed by fusing the cDNAsequence encoding the adhesin portion in-frame to an immunoglobulin cDNAsequence. However, fusion to genomic immunoglobulin fragments can alsobe used (see, e.g., Aruffo et al., Cell 61:1303-1313 (1990); andStamenkovic et al., Cell 66:1133-1144 (1991)). The latter type of fusionrequires the presence of Ig regulatory sequences for expression. cDNAsencoding IgG heavy-chain constant regions can be isolated based onpublished sequences from cDNA libraries derived from spleen orperipheral blood lymphocytes, by hybridization or by polymerase chainreaction (PCR) techniques. The cDNAs encoding the “adhesin” and theimmunoglobulin parts of the immunoadhesin are inserted in tandem into aplasmid vector that directs efficient expression in the chosen hostcells.

Expression of Polypeptides

The polypeptide (e.g., antibody) to be produced using the methoddescribed herein is generally produced using recombinant techniques.

Suitable host cells for cloning or expressing the siRNAs in the vectorsherein are the prokaryote, yeast, or higher eukaryotic cells. Suitableprokaryotes for this purpose include eubacteria, such as Gram-negativeor Gram-positive organisms, for example. Enterobacteriaceae such asEscherichia, e.g., E. coli, Enterobacter, Erwinia, Klebsiella, Proteus,Salmonella, e.g., Salmonella typhimurium, Serratia, e.g., Serratiamarcescans, and Shigella, as well as Bacilli such as B. subtilis and B.licheniformis (e.g., B. licheniformis 41P disclosed in DD 266.710published 12 Apr. 1989), Pseudomonas such as P. aeruginosa, andStreptomyces. These examples are illustrative rather than limiting.

In addition to prokaryotes, eukaryotic microbes such as filamentousfungi or yeast are suitable cloning or expression hosts for polypeptideencoding vectors. Saccharomyces cerevisiae, or common baker's yeast, isthe most commonly used among lower eukaryotic host microorganisms.However, a number of other genera, species, and strains are commonlyavailable and useful herein, such as Schizosaccharomyces pombe;Kluyveromyces hosts such as, e.g., K. lactis, K. fragilis (ATCC 12.424),K. bulgaricus (ATCC 16,045). K. wickeramii (ATCC 24,178), K. waltii(ATCC 56,500), K. drosophilarum (ATCC 36,906). K. thermotolerans, and K.marxianus; yarrowia (EP 402,226); Pichia pastoris (EP 183,070); Candida;Trichoderma reesia (EP 244,234); Neurospora crassa; Schwanniomyces suchas Schwanniomyces occidentalis; and filamentous fungi such as, e.g.,Neurospora. Penicillium, Tolypocladium, and Aspergillus hosts such as A.nidulans and A. niger.

Suitable cultured cells for the expression of glycosylated polypeptideare derived from multicellular organisms. Examples of invertebrate cellsinclude plant and insect cells. Numerous baculoviral strains andvariants and corresponding permissive insect host cells from hosts suchas Spodoptera frugiperda (caterpillar), Aedes aegypti (mosquito), Aedesalbopictus (mosquito), Drosophila melanogaster (fruitfly), and Bombyxmori have been identified. A variety of viral strains for transfectionare publicly available, e.g., the L-1 variant of Autographa californicaNPV and the Bm-5 strain of Bombyx mori NPV, and such viruses may be usedas the virus herein according to the present invention, particularly fortransfection of Spodoptera frugiperda cells. Plant cell cultures ofcotton, corn, potato, soybean, petunia, tomato, and tobacco can also beutilized as hosts.

However, interest has been greatest in vertebrate cells, and propagationof vertebrate cells in culture (tissue culture) has become a routineprocedure. Examples of useful mammalian cell lines include, but are notlimited to, monkey kidney CV1 cells transformed by SV40 (COS-7, ATCC CRL1651); human embryonic kidney cells (293 or 293 cells subcloned forgrowth in suspension culture, Graham et al., J. Gen Virol. 36:59(1977)); baby hamster kidney cells (BHK, ATCC CCL 10); Chinese hamsterovary cells/DHFR (CHO, Urlaub et al., Proc. Natl. Acad. Sci. USA 77:4216(1980)); mouse sertoli cells (TM4, Mather, Biol. Reprod. 23:243-251(1980)); monkey kidney cells (CV1 ATCC CCL 70); African green monkeykidney cells (VERO-76, ATCC CRL-1587); human cervical carcinoma cells(HELA, ATCC CCL 2); canine kidney cells (MDCK, ATCC CCL 34); buffalo ratliver cells (BRL 3A, ATCC CRL 1442); human lung cells (W138, ATCC CCL75); human liver cells (Hep G2, HB 8065); mouse mammary tumor (MMT060562, ATCC CCL51); TRI cells (Mather et al., Annals N.Y. Acad. Sci.383:44-68 (1982)); MRC 5 cells; FS4 cells; and human hepatoma cells (HepG2).

Host cells are transformed with the above-described expression orcloning vectors for polypeptide production and cultured in conventionalnutrient media modified as appropriate for inducing promoters, selectingtransformants, or amplifying the genes encoding the desired sequences.

The host cells used to produce the polypeptide used in the methods ofthis invention may be cultured in a variety of media. Commerciallyavailable media such as Ham's F10 (Sigma), Minimal Essential Medium((MEM), (Sigma), RPMI-1640 (Sigma), and Dulbecco's Modified Eagle'sMedium ((DMEM), (Sigma), or GIBCO® Dulbecco's Modified Eagle Medium;Nutrient Mixture F-12 (Invitrogen) are suitable for culturing the hostcells. In addition, any of the media described in Ham et al., Meth. Enz.58:44 (1979), Barnes et al., Anal. Biochem. 102:255 (1980), U.S. Pat.Nos. 4,767,704; 4,657,866; 4,927,762; 4,560,655; or 5,122,469; WO90/03430; WO 87/00195; or U.S. Pat. No. Re. 30,985 may be used asculture media for the host cells. Other defined or synthetic growthmedia may also be used, and the appropriate medium for growing aspecific type of host cells are known by one of skill in the art ofmolecular and cell biology. Any of these media may be supplemented asnecessary with hormones and/or other growth factors (such as insulin,transferrin, or epidermal growth factor), salts (such as sodiumchloride, calcium, magnesium, and phosphate), buffers (such as HEPES),nucleotides (such as adenosine and thymidine), antibiotics (such asGENTAMYCIN™, hygromycin), trace elements (defined as inorganic compoundsusually present at final concentrations in the micromolar range), andglucose or an equivalent energy source. Any other necessary supplementsmay also be included at appropriate concentrations that would be knownto those skilled in the art. The culture conditions, such astemperature, pH, and the like, are those previously used with the hostcell selected for expression, and will be apparent to the ordinarilyskilled artisan.

Standard cell culture conditions can be used to culture the cells. Cellsare grown and maintained at an appropriate temperature, gas mixture, andpH (such as at about 20° C. to about 37° C., at about 6% to about 84%CO₂, and at a pH between about 5 to about 9). In some embodiments, cellsare grown in an appropriate cell medium at 37° C. for the first 48hours, and shifted to 33° for the next 12 days. Reactions may beperformed under aerobic or anoxic conditions based on the requirementsof the host cells. In some embodiments, the cells are grown using anyknown mode of fermentation, including, but not limited to, batch,fed-batch, or continuous processes.

When using recombinant techniques, the polypeptide can be producedintracellularly, in the periplasmic space, or directly secreted into themedium. If the polypeptide is produced intracellularly, as a first step,the particulate debris, either host cells or lysed cells (e.g. resultingfrom homogenization), is removed, for example, by centrifugation orultrafiltration. Where the polypeptide is secreted into the medium,supernatants from such expression systems are generally firstconcentrated using a commercially available protein concentrationfilter, for example, an Amicon or Millipore Pellicon ultrafiltrationunit.

Kits

The present invention also provides kits comprising compositions andinstructions for use comprising description of the methods of theinvention. The kits can comprise cultured cells, siRNAs, targetsequences, transfecting agents, instructions for the methods of thepresent invention, or any combination thereof.

The following examples are provided to illustrate, but not to limit, theinvention.

EXAMPLES

It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application.

Example 1: Knocking Down of PDHK1, PDHK2, PDHK3, and LDHa ReducesLactate Production and Increases Antibody Titer/Productivity

Materials and Methods

Construction of the Vector Targeting LDHa/PDHK1, 2, 3

Targeting sequence for LDHa was selected as described previously by Kimand Lee et al, Appl. Microbiol. Biotechnol. 74(1):152-159 (2007), andthe LDHa siRNA sequence is CTCGATTCCGTTATCTGAT (SEQ ID NO: 1). To designthe siRNA-targeted sequence for PDHKs, partial cDNA sequences for CHOPDHK1, 2, and 3 were cloned by reverse transcription of polymerase chainreaction (RT-PCR) with primers located within the highly conservedregions of PDHKs. Partially cloned sequences were used for siRNAsequence designing according to the method described by Elbashier et al.(Methods 26:199-213 (2002)).

PDHK1 targeting (siRN sequence:  (SEQ ID NO: 2) GCAGTTCCTGGACTTCGGA PDHK2 targeting (siRNA) sequence:  (SEQ ID NO: 3) CATTCAGTACTTCTTGGAC PDHK3 targeting (siRNA) sequence:  (SEQ ID NO: 4) TGTAGCTGATGTCGTGAAA

The single construct containing targeting sequences for LDHa and PDHKswas constructed using the pSilencer 3.1-H1 hygro vector (Cat#. AM5766,Applied Biosystems/Ambion, Austin, Tex.). LDHa siRNA was inserted intothe KasI site of pSilencer 3.1, with an addition of U6 promoter frompSilencer 2.1 at its immediate 5′ end. SiRNA sequences for PDHK1 and 2siRNAs were inserted into BamHI/HindIII and HindIII sites respectively.A BgIII site was introduced to the 3′ side of PDHK2 siRNA and used forthe insertion of PDHK3 siRNA. For negative control, pSilencer 3.1 vectorcontaining a scrambled siRNA sequence was utilized.

Cell Culture

CHO cells deficient in dihydrofolate reductase (DHFR) were cultured in aproprietary DMEM/F12-based medium in shake flask vessels at 37° C. and5% CO₂. Cells were passaged every three to four days.

Stable siRNA Cell Line (siRNA Clone) Development

A CHO cell line resistant to 25 nM methotrexate (MTX) and expressing arecombinant monoclonal antibody was transfected using Lipofectamine 2000CD (Cat#12566-014, Invitrogen, Carlsbad, Calif.) according tomanufacturer's recommendation (Invitrogen, Carlsbad. Calif.).Transfected cells were centrifuged and seeded into DMEM/F-12-basedselective (glycine-, hypoxanthine- and thymidine-free) medium containing25 nM MTX and 400 ug/ml hygromycin (Cat #10687010, Invitrogen, Carlsbad,Calif.). Re-suspended cells were plated into 96-well plates to generateindividual clones. SiRNA clones were derived from siRNA plasmidtransfection containing targeting sequences for LDHa and PDHKs genes,while mock clones were derived from mock plasmid (Cat#AM5766, AppliedBiosystems/Ambion, Austin, Tex.) transfection containing a scramblesequence designed by manufacture with no appreciable homology to knowngenes.

Quantitative real time PCR (qRT-PCR or Tagman) Analysis

Total RNA from individual clones were isolated using the RNeasy 96 kit(Cat#74181. Qiagen) and were treated with DNase digestion (Cat#79254.RNase free DNase set, Qiagen) to remove residual DNA possibly present inisolated RNA samples. Taqman was performed using universal qRT-PCRmaster mix according to the manufacturer's instructions (Cat#4309169,Applied Biosystems) and expression levels of PDHKs and LDHa werenormalized to housekeeping gene β-microglobulin.

The primers and probe sequences used for Taqman analysis were asfollows:

PDHK1 forward primer:  (SEQ ID NO: 5) GCCCATCTCATCGAAAACAPDHE1 reverse primer:  (SEQ ID NO: 6) AGCCATCTTTAATGACTTCGACTACPDHK1 probe:  (SEQ ID NO: 7) TCGCAGTTTGGATTTATGCTTCCAATGPDHK2 forward primer:  (SEQ ID NO: 8) GATCTGTCCATCAAAATGAGTGA PDHK2 reverse primer:  (SEQ ID NO: 9) TGTGGAGTACATGTAGCTGAAGAGPDHK2 probe:  (SEQ ID NO: 10) CTCTCAATCTTCCTCAAGGGGACACCPDHK3 forward primer:  (SEQ ID NO: 11) CAGCCTGGAGCCTACAAGAPDHK3 reverse primer:  (SEQ ID NO: 12) GGCATACAGTCGAGAAATTGGPDHK3 probe:  (SEQ ID NO: 13) AAGCCATAACCAAATCCAGCCAAGGLDHa forward primer:  (SEQ ID NO: 14) GCCGAGAGCATAATGAAGAALDHa reverse primer: (SEQ ID NO: 15) CCATAGACCCTTAATCATGGTA LDHa probe: (SEQ ID NO: 16) CTTAGGCGGGTGCATCCCATTT β-microglobulin forward primer:(SEQ ID NO: 17) TCCTCTCAGTGGTCT GCT TGG β-microglobulin reverse primer:(SEQ ID NO: 18) TGGCGTGTGTAGACTTGCACTT β-microglobulin probe: (SEQ ID NO: 19) TGCCATCCAGCGTCCCCCAFed-batch Shake Flask Clone Evaluation

Twelve siRNA clones and twelve mock clones were seeded into theproprietary production medium with a pH of 7.15 employing a 14-dayfed-batch culture process with one bolus feed on day 3 and a temperatureshift from 37° C. to 33° C. on day 2. Cell viability and viable cellcounts were monitored by Trypan blue dye exclusion using a Vicell(Beckman Coulter). Lactate concentrations were measured on day 3, 7, 10and 14 using a Nova Bioprofile analyzer (Nova biomedical). The averagecell specific lactate production rate, q_(s) is calculated as the slopeof the graph of integrated total cell number, and the cumulative lactateproduced. [S_(t)−S₀], based on the lactate mass balance equationformulated over the whole culture volume:

S_(t) − S₀ = q_(s)∫₀^(t)Xdtwhere S_(t) is the total amount of lactate in the culture volume (mg) attime t. S₀ is the total amount of lactate in the culture volume (mg) attime t=0, X is the total number of cells in the culture volume at anygiven time t, and q_(s) is the specific lactate production rate inmg/cell/day. Since the above equation is written for the time intervalbetween t=0 and t=t, q_(s) is the average lactate production rate overthis time interval. Per the convention used in this work, if morelactate is produced than consumed by the cell, then the value of q_(s)is positive.Bioreactor Fed-Batch Operation

Bioreactor experiments were performed in 2 L stirred tank bioreactors(Applikon, Foster City, Calif.) operated at 1.5 L working volume. Aftera concentrated nutrient feed at 72 hours post-inoculation, glucose wasadded as needed during the 14-day fed-batch culture. Dissolved oxygenand agitation were maintained in the bioreactor cultures at setpoints of30% of air saturation and 275 rpm, respectively. Culture pH wascontrolled at 7.0 by addition of CO₂ gas or 1 M Na₂CO₃. Culturetemperature was maintained at 37° C. for the first 48 hours, and shiftedto 33° C. thereafter. Process control in each bioreactor was achievedusing a Digital Control Unit from B. Braun Biotech (Allentown, Pa.).

Sample Analyses

Antibody titer was determined using conventional protein A affinitychromatography with UV detection. See Fahrner et al., Biotechnol. Appl.Biochem. 30:121-128 (1999). Culture samples were analyzed for viablecell concentration and viability by Vi-Cell AS cell counter (BeckmanCoulter, Fullerton, Calif.), pH and lactate by Bioprofile 400bioanalyzer (Nova Biomedical, Waltham, Mass.), and osmolality by amulti-sample osmometer (Advanced Instruments, Norwood, Mass.).

Statistical Analysis

Two tailed student t-test was carried out using JMP software.

Results

Construction of a siRNA Vector Targeting PDHKs and LDHa

There are four PDHK genes reported by Harris et al. (Adv. Enzyme Regul.42:249-59 (2002) in mammalian cells. To assess if all four PDHK genespresent in CHO cells, four sets of RT-PCR primers were designed based onthe conserved regions between human and mouse PDHK sequences. The PCRresults revealed that even though all four PDHK mRNAs can be detected inCHO cells, PDHK4 mRNA level is minimal and much lower than other 3 PDHKsin DHFR-deficient (dihydrofolate reductase-deficient) CHO cells. Hence,only the expression of PDHK1, 2, and 3 genes was knocked down along withLDHa gene. For LDHa and each PDHK, three siRNA sequences were designedand tested in CHO cells to choose the siRNA sequence exhibiting bestdown-regulation of the target gene. The best siRNA sequence for LDHa wasselected based on the findings by Kim and Lee. Appl. Microbiol.Biotechnol. 74(1): 152-9 (2007). The siRNA sequence for LDHa and PDHKswere constructed in a single vector where siRNA for LDHa was under thecontrol of U6 promoter, whereas siRNAs for each PDHK were driven by H1promoters (FIG. 1).

Generation of Stable Clones with Reduced Expression of PDHK1, 2, 3, andLDHa

The siRNA construct targeting PDHKs and LDHa was transfected into CHOcells expressing a monoclonal antibody to get individual clones namedsiRNA clones. Individual siRNA clones were assayed for mRNA expressionof four genes, PDHK1, 2, 3 and LDHa, using Taqman analysis. Twelve siRNAclones that exhibited most reduced expression of above four genes wereidentified (FIG. 2) for further analysis. The mock vector containingscramble sequence was also transfected into the same antibody expressingcells to get individual clones named mock clones. Twelve mock cloneswere chosen randomly as control and their mRNA expression levels of LDHaand PDHK1, 2, and 3 genes were also analyzed by Taqman. On average, themRNA expression levels for LDHa, PDHK1, 2, and 3 in selected twelvesiRNA clones were reduced by 90%, 32%, 83%, and 70% respectivelycompared to mock clones (FIG. 2).

Fed-Batch Shake Flask Evaluation of siRNA and Mock Clones

(a) Reduced Lactate Levels and Higher pHs in Culture Media Observed insiRNA Clones

To evaluate the effect of siRNA-mediated down-regulation of LDHa andPDHKs on lactate production, 12 siRNA and 12 mock clones were evaluatedin shake flask vessels in our proprietary medium employing a 14-day,fed-batch, and temperature shift process. The experiment has beenrepeated for three times and similar results were observed. The resultsfrom one set of experiment is shown as representatives in the figures.The results showed that compared to mock clones, siRNA clones hadreduced lactate levels (FIG. 3) in general. By day 14, siRNA clonesshowed 91% less lactate in average than mock clones (p<0.0001) (FIG.3A). Consistent with the lower lactate level in siRNA clones over the14-day production period, the average lactate production rate for siRNAclones was negative 0.02 mg/10⁶ cells/day, suggesting that lactatesynthesis rate is lower than the consumption rate. In contrast, theaverage lactate production rate was 0.01 mg/10⁶ cells/day for mockclones, indicating the overall lactate synthesis rate is higher than theconsumption rate. This difference in lactate production rate betweensiRNA and mock clones was statistically significant (p<0.002) (FIG. 3B).Since lactate level in the media affects pH, by day 14, the average pHfor mock clones dropped to 6.54, whereas the average pH for siRNA cloneswas 7.04 (FIG. 3C). The observed lower average pH is in agreement withhigher average lactate level for mock clones.

b) Increased Antibody Titer and Specific Productivity (Op) Observed insiRNA Clones

To investigate whether knocking down gene expression of PDHKs and LDHaaffect antibody production, samples were collected from fed-batch shakeflask experiments on day 3, 7, 10 and 14 to measure antibody titers byprotein A chromatography. The data showed that, on average, siRNA clonesproduced 68% more antibody that that of mock clones (FIG. 4A, p<0.022),and average cell-specific productivity (Qp) measured in pg/cell-d forsiRNA clones was 75% higher than that for mock clones (FIG. 4B,p<0.006). To evaluate cell growth, shake flask samples were collected onday 3, 7, 10, and 14 to measure viable cell counts and viabilities tocalculate integrated viable cell count (IVCC). In contrast to antibodytiters and Qps, no appreciable cell growth differences were observedbetween the two groups (FIG. 4C). Antibody product quality attributesincluding glycan profile, charge variants and percentage of aggregationwere comparable between siRNA and mock clones.

Bioreactor Fed-Batch Culture Evaluation of siRNA Mock Clones

Since pH-controlled fed-batch bioreactor culture is the standardscale-down model for large scale manufacturing, the performance of somesiRNA and mock clones in 2 L bioreactors was further investigated. Giventhe limitation in bioreactor availability and experimental complexity,12 siRNA and 12 mock clones in duplicates were not run due toimpracticability. Two representative siRNA clones and two representativemock clones whose metabolic profiles best represented the averageperformance for each group to minimize selection bias, along with theparental line used for siRNA and mock plasmid transfections for 21,bioreactor evaluation were selected. Cell culture samples were collecteddaily (except on days 6 and 13) for lactate, glucose, osmolality, andtiter analysis. The lactate levels for siRNA clones generally remainedflat whereas the lactate levels for mock and parental clones continuedto increase during the 14-day production period. On day 14, the twosiRNA clones had 86% lower lactate level on average in media than mockclones or parental clone (FIG. 5A) and had lower specific lactateproduction rate than mock clones and parent line (FIG. 5B). Similarly,the osmolarities for siRNA clones remained around 300 mOsm whereas theosmolarities for mock clones or parental clone continued to increaseduring the 14-day production period. On day 14, average osmolarities for2 siRNA clones were 60% lower than those of mock and parent clones (FIG.5C). Importantly, on day 14, the siRNA clones on average produced 125%more antibody than that of mock clones (FIG. 6). As observed infed-batch shake flask evaluation, siRNA and mock clones have comparableviabilities and cell growth in 2 L bioreactors.

Discussion

Previous study demonstrated that down-regulating LDHa gene expressionalone was able to reduce lactate production. Kim and Lee, Appl.Microbiol. Biotechnol. 74(1): 152-9 (2007). However, in their studydespite the 45-79% reduction in lactate level, there was no significantimprovement in Qp and product titer suggesting that knocking down LDHaalone in CHO cells is not sufficient to improve Qp and product yieldefficiently. Further, simultaneously down-regulating PDHK1, 2, and 3 inCHO cells was neither sufficient to reduce lactate level nor to increaseantibody productivity. Since the only way for cells to generate lactateis through pyruvate reduction, and pyruvate can not only be converted tolactate by LDH but also be converted to acetyl-CoA by PDH entering TCAcycle to be oxidized, reducing lactate production by knocking down LDHaexpression and promoting pyruvate into TCA cycle by knocking down PDHKsmay synergize to reduce lactate level and to provide cells with moreenergy and possibly metabolic intermediates leading to increasedantibody production.

The expression of LDHa, PDHK2, and PDHK3 was substantially reduced andthe expression of PDHK1 was moderately reduced in all clones tested. Themoderate reduction in PDHK1 expression is likely due to non-optimumsiRNA targeting sequence since moderate reduction was observed withthree PDHK1 siRNA sequences tested. Variations on lactate production andantibody production in mock and siRNA clones were observed, since eachclone had different expression levels of LDHa and PDHKs. Nevertheless,by day 14, the average lactate level in siRNA group was lower than thatin mock group leading to the lower average pH for mock clones than thatof siRNA clones in fed-batch shake flask culture. More importantly, inaddition to lower specific lactate production rate, the average titerand Qp for siRNA clones increased by 68% and 75% respectively comparedto those of mock clones with no noticeable differences in cell growthand product quality between siRNA and mock clones. Interestingly, forthe day 14 titers versus day 14 lactate levels, there was a good inverserelationship between titers and lactate levels among mock clones, butnot among siRNA clones. The observed differences in titers and lactatelevels among mock clones may be likely that parental clone isheterogeneous in antibody productivity and cellular metabolism eventhough the cell line was derived from a single clone. A total of 12 mockclones were evaluated to take into consideration of clonal variation.The data indicate that knocking down LDHa and PDHKs simultaneouslyreduces lactate level and improves antibody production in CHO cells.Hence, for the development of robust and productive antibody productionprocesses, simultaneous down regulation of both LDHa and PDHKs providesan efficient approach.

The performance of 2 mock and 2 siRNA clones in 2 L bioreactors withduplicates was further investigated. Those 4 clones were selected tobest represent the average productivity in each group based on fed-batchshake flask evaluations. Similar to the observations from shake flaskexperiment, the siRNA clones had lower lactate levels and higher titersthan mock clones in 2 L, bioreactor evaluation. Given that pH iscontrolled in fed-batch 2 L bioreactors, the mock cultures exhibitedincreased osmolality than siRNA cultures since higher lactate levels inmock clones needed more alkali addition to maintain set point pH.

In summary, the data from fed-batch shake flask and 2 L, bioreactorevaluations demonstrated that simultaneous knockdown of LDHa, PDHK1, 2,and 3 in CHO cells is effective in reducing lactate level and inincreasing antibody titer without impacting cell growth and productquality.

What is claimed is:
 1. Cells in culture comprising a first heterologousnucleic acid sequence encoding a first small interfering RNA (siRNA)specific for a lactate dehydrogenase (LDH) and a second heterologousnucleic acid sequence encoding a second siRNA specific for a pyruvatedehydrogenase kinase (PDHK), wherein the first heterologous nucleic acidsequence is operably linked to a first promoter, and wherein the secondheterologous nucleic acid sequence is operably linked to a secondpromoter, wherein the cells have a polypeptide productivity of at leastabout 68% higher than cells without the heterologous nucleic acidsequence comprising siRNA specific for LDH and siRNA specific for PDHK.2. The cells of claim 1, wherein the cells further comprise a thirdheterologous nucleic acid sequence encoding an siRNA specific for asecond PDHK and wherein the third heterologous nucleic acid sequence isoperably linked to a third promoter.
 3. The cells of claim 2, whereinthe cells further comprise a fourth heterologous nucleic acid sequenceencoding an siRNA specific for a third PDHK and wherein the fourthheterologous nucleic acid sequence is operably linked to a fourthpromoter.
 4. The cells of claim 3, wherein the cells further comprise afifth heterologous nucleic acid sequence encoding an siRNA specific fora fifth PDHK and wherein the fifth heterologous nucleic acid sequence isoperably linked to a fifth promoter.
 5. The cells of claim 1, whereinthe PDHK is selected from the group consisting of PDHK1, PDHK2, PDHK3,and PDHK4.
 6. The cells of claim 1 wherein the PDHK is selected from thegroup consisting of PDHK1, PDHK2, and PDHK3.
 7. The cells of claim 1,wherein the PDHK is selected from the group consisting of PDHK1 andPDHK2.
 8. The cells of claim 1, wherein the PDHK is selected from thegroup consisting of PDHK1 and PDHK3.
 9. The cells of claim 1, whereinthe PDHK is selected from the group consisting of PDHK2 and PDHK3. 10.The cells of claim 3, wherein the LDH is LDHa, wherein the first PDHK isPDHK1, wherein the second PDHK is PDHK2, and the wherein the third PDHKis PDHK3.
 11. The cells of claim 1, wherein the cells produce aheterologous polypeptide.
 12. The cells of claim 11, wherein theheterologous polypeptide is an antibody.
 13. The cells of claim 3,wherein the cells have an average lactate production rate of less thanabout negative 0.02 mg/10⁶ cells/day.
 14. The cells of claim 3, whereinthe cells have a Specific Productivity of at least about 75% higher thancells without the heterologous nucleic acid sequence comprising siRNAspecific for LDH and siRNA specific for PDHKs.
 15. The cells of claim 3,wherein the cells have an osmolality at less than about 300 mOsm. 16.The cells of claim 11, wherein the cells are mammalian cells.